Behaviour & Policy, Connections in Transportation

11.478/11.158 Final Term Report [Group 6] - REVISIONS Avital Baral, Mark Bennett, Mary Hannah Smith, Ashutosh Singhal 19 May 2019

Do[n’t] Stop Me Now How intersection and information design influences vehicle yielding behavior

HIGHLIGHTS •

Physical interventions, such as raised intersections & extended curbs are more effective than informational signage for increasing driver yielding rates

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Most informational signage showed no additional impact over no signage

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Street width at crosswalk is an important predictor of yielding rates

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Physical interventions can be more costly and complicated for public officials to implement

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There is a need for officials to determine a conclusive legal interpretation of Massachusetts state law

ABSTRACT All licensed drivers in Massachusetts must affirm they know the rules of the road, yet despite laws requiring vehicles to yield to pedestrians at crosswalks, we see these rules broken often. So how do we improve compliance and safety? This project explores how physical and information design can change behavior.

Pearl and Brookline Streets in Cambridgeport offer a unique opportunity to conduct a natural experiment studying the effects of information and street design on vehicle yielding rates. Both streets feature fairly uniform width and surrounding context but offer a wide array of intersection design and information techniques to prompt vehicles to yield to pedestrians. The core of this project was a standardized observation/experimental procedure to observe vehicle yielding behavior. The study authors systematically attempted a series of crossings at selected intersections, while keeping a tally of vehicle yield rates. The procedure was tested on seven different intersections over two different days. We then observed trends and ran regression analyses to identify patterns in yielding rates. Finally, we conducted an interview on the topic with City of Cambridge staff.

The main findings of our experiment were that stop signs and tabletop designs resulted in the highest vehicle yielding rates. Excluding stop signs and tabletops intersections, the relative width of the intersections was the only significant factor, accounting for 80% of the variability in the vehicle yielding rates (narrower intersection conditions were correlated with higher yielding rates). Further experiments with greater sample sizes are needed to ascertain the robustness of our results.

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PROBLEM STATEMENT - Purpose, Significance, Research Questions & Hypotheses According to the 2018 Pedestrian Safety Report by the Governors’ Highway Safety Association (GHSA), more than 6,200 pedestrians were killed in crashes last year—a sharp 50% increase in just the past 10 years.

Researchers and safety experts have pointed to increased VMT and increased distractions over the past decade as possible explanations, but conclusive data has yet to be found. We do know however that a common point at which pedestrians and vehicles come into potential conflict is at intersections and crossings.

Almost every state in the US requires drivers to yield to pedestrians in uncontrolled crosswalks, including Massachusetts. But any pedestrian knows compliance with this law can be low. Drivers failing to yield to pedestrians can increase the risk of a dangerous crash. This research looks to better understand how driver behavior can be improved to yield more frequently.

There exist a variety of “prompts” at intersections to signal the oncoming vehicle to slow down and yield for pedestrians. The purpose of this study is to identify which design and information elements prove more helpful or less helpful in prompting drivers to yield for pedestrians. Consequently – we question how physical and information design at intersections can change driver behavior to better comply with regulations, in the interest of the safety of pedestrians. This study looks to Pearl and Brookline Streets in Cambridge, MA, where many different street geometry and information design tactics are used within relatively short road lengths.

We hypothesize that different street and information design can, in fact, prompt different driver behavior.

We believe that higher yielding rates at street intersections will help make roads safer for pedestrians. The lessons from this study could consequently be applied to intersections well beyond Cambridge, creating a safer environment for both the driver and the pedestrian.

LITERATURE REVIEW Pedestrian Safety Research on Crosswalks: The literature on pedestrian safety is vast, covering user behavior, education, enforcement and modifications of the built environment. On the specific topic of intersection design, Turner et al. found that crosswalk red signal or beacon devices led to a yield rate of 95%, more effective than other surveyed options such only paint or only stop signs. Small R1-6 “yield for pedestrian” signs were found to achieve yield rates of up to 88-92%, compared to 0-40% at the same intersections prior to sign installation (Van Houten et al., 2018). Bennett et al. corroborated the effectiveness of small yield signs, and the findings of Turner et al., showing that gateway signs produce comparable yielding rates to those of beacons, but are a more cost-effective option; gateway positioning creates perception of narrowed travel lanes, which slows down drivers and makes it more likely that they stop for pedestrians. Raised intersections were also found to be an effective intervention to increase pedestrian safety by reducing vehicle speeds (Perkins+Will Consultant Team; King). The City of Cambridge evaluated the effectiveness of a tabletop installed at a local intersection and found that motorist yield rates increased from 10% to 55% (FHWA “Traffic Calming 29.”).

However, other researchers found that while local residents believe signs and signals increase traffic safety, in reality these interventions are ineffective at preventing serious crashes. They reference a large survey of crashes in NYC that found “most deaths were caused not by lack of signal and signs; they occurred after people driving vehicles have ignored these controls or violated numerous other rules of the road” (Sadik-Khan, J., & Solomonow, S. 2016).

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Bias and Behavioral Reasoning behind Vehicle-Pedestrian Yielding Rates: The literature highlights the persistence of implicit racial biases in vehicle yielding behavior. Goddard et al. found that more drivers passed black men than white men waiting to cross, black men had to wait longer to cross, and that the pedestrian fatality rate for Hispanic and black men from 2000 to 2010 was twice the pedestrian fatality rate of white men. Driver wealth may also impact their pedestrian yield rate, as one study found that drivers with nicer cars were significantly more likely to cut off pedestrians in intersections (Piff et al.). Driver yield rate is also influenced driver distractions, and in 2015, it was found to impact “10% of fatal crashes and 15% of crashes with an injury” in the US (Vision Zero Plan, pg. 12).

Road Design Safety Research: Outside the scope of our study, there exists literature on the modification of the road environment/vehicle domain in order to reduce vehicle crashes, noting the mixed and sometimes counterintuitive results of road modifications. Retting et al. found that “highly effective countermeasures include single-lane roundabouts, sidewalks, exclusive pedestrian signal phasing, pedestrian refuge islands, and increased intensity of roadway lighting. Other countermeasures, including advance stop lines, in-pavement flashing lights, and automatic pedestrian detection at walk signals, are promising but have been evaluated on a more limited basis.” They also noted that reducing vehicle speed does not necessarily reduce pedestrian-vehicle crashes. In general, Dumbaugh & Li noted that the principle of “forgiving design”, intended to reduce “run off the road” crashes, prioritizes the safety of motorists over that of pedestrians. They denounce the assumption that driver error is random, which leads to planners discounting ways in which design affects traffic fatalities.

Best Practices in Street Design in Cambridge: In 2016, the City of Cambridge adopted Vision Zero standards for its streets (City of Cambridge, 2019). Vision Zero is “a guide to planning, designing and building streets that can save lives” with the goal of zero trafficrelated fatalities and severe injuries (Vision Zero Streets). The city’s Vision Zero Action plan includes a number of design goals that the city would like to implement. It recommends removing obstacles blocking the view of side streets and of crosswalks, and restricting parking near crosswalks. It does not explicitly mention sign design in its plan or recommendations (City of Cambridge, 2017).

As part of the City of Cambridge Vision Zero Plan, the city mapped out pedestrian crashes that required ambulance transport during the period from 2015-2016 (City of Cambridge Police Department, 2017). The map is shown below, and the study area relevant to this project is not highlighted as a crash hot-spot.

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Figure 1: Study Area

An older report from 2000 on Pedestrian Safety in Cambridge focused on best practices for traffic design.

Notably, it was drafted by the City Design and Development department rather than the Traffic, Parking & Transportation Department. It notes that while the design of many street elements is regulated by state and federal standards, the city has discretion in deciding which street elements to use in certain locations. Wider sidewalks with narrower traffic lanes, curb bump-outs, and curved streets are all concepts that can reduce traffic, and therefore increase pedestrian safety. The report recommends side-mounted “Yield to pedestrian” signs only where aspects of the crossing location make special safety conditions, and “Pedestrian crossing” signs should be installed in areas with high-pedestrian volume. No other sign types are mentioned. The report also mentions several advantages of using raised tables as crosswalks, including that they “slow traffic”, “remind drivers of the crosswalk”, “encourage pedestrians to use the crosswalk” and “pedestrians do not have to contend with curbs” (City of Cambridge, 2000). This is report is relevant to our research because it describes the guidelines that may have informed the city when they intervened along Brookline St., which has not been recently updated by the City Traffic Department.

State and Local Laws on Pedestrian Crossing: State law in Massachusetts dictates that drivers are obligated to yield to pedestrians if the pedestrian is on the same half of the road occupied by the car. The full law reads: “When traffic control signals are not in place or not in operation the driver of a vehicle shall yield the right of way, slowing down or stopping if need be so to yield, to a pedestrian crossing the roadway within a crosswalk marked in accordance with standards established by the department of highways if the pedestrian is on that half of the traveled part of the way on which the vehicle is traveling or if the pedestrian approaches from the opposite half of the traveled part of the way to within 10 feet of that half of the traveled part of the way on which said vehicle is traveling.” (Massachusetts General Laws, Part I, Title XIV, Chapter 89, Section 11)

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However, this law is open to interpretation by local officials. The City of Cambridge refers to the state law in their report on pedestrian safety (2000), but does not mention the caveat that drivers only have to yield when pedestrians are in their half of the roadway. Their interpretation reads: “At all marked crosswalks, state law requires that the driver of a vehicle yield the right of way to a pedestrian in the crosswalk, unless the vehicle has a green light and is not turning. Pedestrians should not enter a crosswalk unless it is safe to do so, and they should never assume that a driver will obey the law and stop. Pedestrians should step into the crosswalk to signal their intention to cross, look left, right, then left again, and when vehicles stop, cross.”

Meanwhile, the Boston Complete Streets Guidelines claim that state law does not cover cases where crosswalks are unmarked at unsignalized intersections. Their full statement says: “Unfortunately, Massachusetts laws are silent on the rights of pedestrians in unmarked crosswalks at locations that are not signalized. In most other states, the right-of-way is granted to pedestrians in unmarked crosswalks.”

METHOD Natural Experiment We selected seven intersections along Pearl and Brookline Streets in Cambridge (See appendix 3 & 4). Both streets are one-way, and each intersection is +-shaped, with T-shaped intersections excluded from this study to eliminate a further variable. Figures 2 and 3 show a pair of intersections included in the study and offer context for the surrounding environment of the study area.

Figure 2: Painted Crosswalk with One Ped Crossing Sign and Curb Bump Out (Brookline at Hamilton)

Figure 3: Painted Crosswalk with One Ped Crossing Sign + Raised “Tabletop” Intersection (Brookline at Erie)

Data Collection Process 5

Intersection design effectiveness was evaluated by observing how many drivers in engine-powered vehicles yielded for pedestrians at each intersection compared to how many total vehicles passed through.

Each intersection was initially evaluated for one hour on a weekend day. Each intersection was evaluated for two half-hour periods by two different evaluators. Upon this first round of evaluations, the research team concluded a strong sample could be collected in less time. The second evaluation took place on a weekday during PM peak travel time, and each intersection was evaluated for two 20-minute periods by two different evaluators. In total, each intersection was observed by four different evaluators.

The research team consists of four members: One undergraduate student and three graduate students. Team members acted as evaluators, and each evaluator had the opportunity to observe each intersection. For each time period, each intersection was observed by both one of the two tallest team members and by one of the two shortest team members to help eliminate or identify variances based on individual evaluators.

For each intersection, the evaluator first collected a five-minute sample of cars passing through the intersection. This count allowed us to later control for traffic volume.

Each crosswalk in the study included a plastic or metal plate near the edge of the sidewalk right before the street pavement begins. These plates are indicators for visually-impaired persons that they are about to enter a street. For our purposes, these plates served to standardize the evaluation process. For each intersection, evaluators positioned themselves on a plate with their body at a 15-45-degree angle to the road’s edge, turned towards approaching vehicles. This position both indicated to vehicles the intention to cross while also allowing the pedestrian to safely observe vehicle behavior and make eye contact with vehicle operators.

Figure 4: Experimental Design

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Evaluators were instructed to otherwise keep their arms at their sides and feet planted on the ground.

Evaluators were instructed to step away from the sidewalk’s edge if at any point they felt uncomfortable with an approaching vehicle. Each evaluator counted the number of vehicles that pass through each intersection.

The evaluator also counted the number of vehicles that safely yielded for them. When the evaluator confirmed a vehicle had safely yielded to them, they crossed the intersection to the other side.

The evaluator then removed themselves from the immediate intersection area until any other vehicles that may have observed the crossing proceed through the intersection. This “reset” the observation. The cars that passed through while the observation was being reset were not counted. The evaluator then once again positioned themselves on a crosswalk plate and replicated the above process. By this process, the evaluator ended up crossing back and forth throughout the observation period, allowing the research team to observe any possible differences with standing at the left or the right side from a vehicle perspective. The evaluator repeated these steps for 25 minutes at each intersection during the first weekend condition and for 15 minutes during the weekday condition.

Many other types of data could have been collected as part of this experiment, including attributes about the driver and their car, as well as information about the evaluators like race and height, which might impact driver yield rates. We ultimately chose to limit our evaluation to yield rate due to perceived limitations in the amount of data a single evaluator could actually capture from each interaction, and our desire to focus on aspects of street design rather than the myriad of potential individual characteristics that could impact driver behavior. Having said that the evaluator’s gender was noted in our data collection, as well as the exact time and day of the observations.

Qualitative Interview with the of City of Cambridge This study also included an interview with City of Cambridge Traffic, Parking and Transportation staff to better understand the city’s reasoning behind the variety of intersection and information designs observed on Pearl and Brookline Streets. (See appendix 2 for interview questions.)

Broadly, we learned that the diversity of treatment of different intersections was perhaps not as intentional as we had expected. City staff acknowledged that signage does little to improve driver yielding rates and informed us that most signs have been put up on the request of residents. The city has installed signs in many places largely because they increase the “feeling of safety”, as opposed to actual yielding rates. Thus, each intersection design may be the result of the type of requests of local intersection residents. Some intersection design however was intentional on the part of the city. For instance, the intersection at Pearl St & Putnam Avenue has stop signs due to the high traffic volumes along Putnam Avenue.

City staff further explained that curb extensions on some intersections were primarily done for the accommodation of the tree roots. However, here too, there is a lot of tension between some residents wanting the extensions, while others are more concerned about losing their parking spots. Furthermore, while it is predominantly a residential street, there are occasional trucks coming through, and the city needs to pay attention to any difficulty navigating through the extended curbs. City staff added that they generally prefer to simply put in signage/markings as it is much easier to install, cheaper, and less maintenance. However, one must be cautious of signage clutter, which can become overwhelming for the driver.

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Thus, while curb extensions are a great solution for pedestrian safety, their implementation can be tricky.

Similarly, the tabletop intersection presents similar issues of cost and time and also bring a new challenge of solving the stormwater drainage on site due to the existing lower levels of drain lines.

Lastly, we also discussed legal requirements. City staff mentioned that their interpretation of the state law was that a vehicle must yield to a pedestrian crossing at both marked and unmarked intersections – regardless of the presence of any signage/crosswalk paint. This runs counter to the interpretation of state law made in Boston’s 2013 Complete Streets Guidelines. Furthermore, there is a lack of clarity of when a vehicle must yield to the crossing pedestrian. According to the law, a vehicle must yield only if the pedestrian has already entered the crosswalk. It’s unclear whether this means the pedestrian must step into the street before a vehicle is required to yield—an action we believe many pedestrians would consider less than safe.

Barriers and Issues Pearl and Brookline Streets were chosen because they offer fairly uniform surrounding environments, street widths, tree canopies, street parking and speed limits. This allowed us to remove a number of variables from consideration. Additionally, we had to overcome the barrier of potential additional confounding factors like difference in the time of day, traffic volumes or physical characteristics of the pedestrian. And so, each intersection was studied by two researchers of different heights, and all intersections were evaluated on a weekend and a weekday. Finally, traffic counts were collected at each intersection prior to study so as to control for the number of cars passing through. To control for crossing width, we also measured each crosswalk during the second evaluation. A final barrier that proved difficult to overcome was accounting for the presence of parked cars. This variable deserves further research.

RESULTS & INTERPRETATIONS Intersection Pearl at Putnam Brookline at Erie Brookline at Allston Brookline at Hamilton Brookline at Chestnut Brookline at Franklin Pearl at Allston

Width (ft)

Stop Signs

23.37

14.75

One Ped Sign + Raised Intersection

23.37

23.75

Cars Observed 67 135

One Ped Sign + Blinking Light (bump out)

16.93

23.75

145

76

52.41%

One Ped Sign (bump out)

17.90

26.25

146

76

52.05%

Two Ped Signs + State Law

23.39

26.5

132

48

36.36%

Treatment

Cars Per 5 Min

Cars Yielded 65 99

Yield Rate 97.01% 73.33%

99 33 33.33% 78 12 15.38% "Gateway" Two Ped Signs 26.25 11.75 Standard Deviation of Proportions: .27 Figure 4: Results Table. See appendix 5 for more detailed statistics from each evaluation Only Painted Crosswalk

26.74

23.75

Stop Sign: Not surprisingly, a stop sign produced the best yielding rates. We noticed that most vehicles slowed down or halted regardless of any pedestrian attempting to cross – which consequently resulted in a high yielding rate. However, we acknowledge that the city cannot have stop signs at every intersection which could create issues of traffic flow as well as increased carbon emissions.

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Raised Intersection: The raised intersection “tabletop� condition resulted in very high yielding rates. We believe the design that forces vehicles to ramp up slightly makes drivers take extra caution.

Blinking Light/ Bump-Out: A high yielding rate, although the curb bump-out present makes it difficult to determine whether the blinking light is making any impact. This intersection also immediately followed a fourway stop intersection, which may have contributed to slower approaching vehicles. On the other hand, the curb extension was also fronted by a parked vehicle, which obscured the pedestrian from view.

Figure 5: Confounding factors. Parked vehicles, like this one at Brookline and Allston, may have influenced observation results.

One Ped Sign/ Bump-Out: Similar to the previous intersection, a high yielding rate. Once again, a short crossing as a result of a curb bump-out.

Two Ped Signs + State Law: One might assume the presence of extra signage explaining the state law requiring cars to yield might persuade cars to yield. However, we observe a fairly poor yielding result here. We also observed generally higher vehicle speeds, although we had no good explanation for this. Finally, the state law signs themselves hung low and appeared to potentially hide the pedestrians from view.

Figure 6: Backside of State Law Sign. At Brookline and Chestnut, the signage may have actually blocked the view of the pedestrian

Only Painted: We assumed this intersection as our best control: No bump-outs, raised intersection or signage.

We observed about 1/3 of all cars yielding here, although our somewhat lower sample size is low due to the fact that in our peak travel observation, traffic backed up into this intersection occasionally, putting the observation on pause. This could affect our final results.

Gateway: One might rationally assume that this intersection would have a higher yield rate than one sign.

However, the yielding rates here are confoundingly low at 15%. Extraneous factors not immediately apparent may be present.

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Figure 8: Yielding Rates Variation

Analytical Methods Analytical Framework: There are many factors that could be influencing drivers’ decisions to yield, including: Failure to realize they are approaching a crosswalk, failure to see the pedestrian because the vehicle is driving too fast to spot the pedestrian in time/ yield in time, ignorance of the law, lack of interest in yielding even though the driver knows the law. This study was unable able to test for the final factor, but this study can begin to test the first three.

Warning signs and lights can act as increased indicators of approaching crosswalks. Raised intersections and curb bump-outs can both slow down vehicle speeds and bring the pedestrian into better view. Finally, we examined a treatment where the state law is actually spelled out in a sign. This analysis seeks to compare design elements against these behavioral factors and then empirically check each design element.

This study was conducted as a proof of concept and thus was unable to achieve large enough sample sizes at each intersection for us to broadly and reliably test statistical significance. That being said, some clear patterns emerged in our interpretation, and our goal was to push statistical and analytical modeling as far as we felt this study’s sampling and limitation could go.

One variable we made sure to account for was the difference in behavior depending on day of the week. We tested each intersection twice on the weekend in moderate traffic and twice on a weekday at the PM peak in heavy traffic. We found no consistent results between weekday and weekend behavior. Some intersections saw higher yielding rates on the weekend and some on the weekday.

Intersection Pearl at Putnam Brookline at Erie Brookline at Allston Brookline at Hamilton Brookline at Chestnut Brookline at Franklin Pearl at Allston

Treatment Stop Signs One Ped Sign + Raised Intersection One Ped Sign + Blinking Light (bump out) One Ped Sign (bump out) Two Ped Signs + State Law Only Painted Crosswalk

"Gateway" Two Ped Signs Figure 7: Weekday vs Weekend Yield Rates

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Weekend Yield Rate 94.9% 76.8% 51.4% 48.7% 32.9% 35.6% 20.5%

Weekday Peak Yield Rate 100.0% 69.7% 53.5% 55.7% 40.7% 30.0% 10.3%

Bivariate Regression Modeling and Correlations: With our previously caveats on sampling limitations in mind, we did still run bivariate regressions to examine how different design and information independent variables affected our dependent variable: yielding rate.

With all seven intersections included in the model, we found no single variable effected yielding rates in a statistically significant way (see appendix 6). Observing that the stop sign condition appeared to be uniquely effective, we removed the intersection of Pearl and Putnam and ran bivariate regressions on the remaining six intersections. Once again, no statistically significant factor was identified (see appendix 6).

Further, we reasoned that, observationally, the stop sign and raised intersection were clearly impacting yielding rates in a positive fashion. There also appeared to be clearer causal mechanisms at work with these two intersections. What was less obvious was why the remaining five intersections were leading to different yielding results, but width appeared to be linked. Below is the comparison between street width and yielding rate. While the two narrowest intersections feature curb bump-outs, the design element is not required for narrow width.

Figure 9: Street Width by Yield Rate

Finally, we needed to test for the impact the volume of traffic on yielding rates. As the regression analysis below shows, there is no strong connection: Bivariate regression analysis for traffic volume, all intersections

Regression Statistics Multiple R 0.01883289 R Square 0.00035468 Adjusted R Square 0.19957439 Standard Error 0.29702819 Observations 7 Figure 10: Regression Statistics

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DISCUSSION As expected, the stop sign treatment and raised intersection treatment performed noticeably better. With only a crosswalk and no signage or further design treatment, cars yielded just over 35% of the time. That rate was more than doubled at the raised intersection. A single pedestrian sign resulted in yielding rates of almost 50%, although regression modeling later found this effect was due to the short crossing distance at our intersection with one pedestrian sign. There did not appear to be a noticeable difference with a blinking light.

Once we removed the most reliable yielding mechanisms (stop signs and tabletops) from the regression analysis, intersection width was the only statistically significant influence on the yield rate. In fact, information signs, blinking lights, and other street design elements had no statistically significantly impact the yield rates.

Observationally, we noted that stop signs were important in impacting yield rates because cars would almost universally stop at the intersection even if no pedestrian was attempting to cross, but this effect was not shown in our regression analysis; we suspect that this could be revealing a problem with our analysis or that our sample size may be too low.

Additionally, we have concerns about the possible ambiguity of the law regarding the obligations of drivers at intersection. It is plausible that drivers themselves are unaware of whether or not they must yield at a given intersection. In fact, neighboring municipalities themselves appear to be in disagreement with interpreting the law. Boston appears to state that pedestrians have no protection in unmarked crosswalks, while Cambridge officials told us they operate under the understanding that they do. Further, a close reading of the state law appears to say that pedestrians must actually leave the curb and be in the street for cars to be required to stop. Cambridge city officials communicated this was their belief too. However, this strikes us as unreasonably dangerous for the pedestrian to be required to enter to street before the car actually yields. This ambiguity might mean that our assumptions that all drivers know the law and know when to yield is more complicated.

Significant issues did occur while testing two intersections. At Pearl and Allston, evaluators reported the surrounding environment partially hid them to the view of traffic. We believe the poor yielding results at this intersection may partially be a result of those additional environmental factors. Additionally, evaluators also reported poor visibility conditions at Brookline and Chestnut. A slight hill made it more difficult for approaching vehicles to see around parked cars. For reasons not immediately clear, vehicles also passed through this intersection at an apparently much higher speed than other intersections. Finally, the state law explanation signs actually significantly (and ironically) obscured the evaluators from view of vehicles while trying to cross. For these reasons, we feel it’s more difficult to make conclusions about these intersections and their design conditions.

One final observation: Although no data was collected, there appeared to be a strong copycat effect among cars. If a long line of cars was approaching and the first car did not stop, rarely did any of the immediately following cars yield.

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Impact and Implications This study offers a pathway for future, more robust studies to examine different intersection designs in similar contexts. However, we do feel confident in our findings that street width is a significant factor in increasing vehicle yielding. This result indicates that curb bump-outs may be extremely useful tools for intersections where poor yielding is a safety issue. However, cheaper paint, planter and flexipost options exist to decrease width as well. Further, we feel confident that the raised intersection is a reliably useful method for slowing vehicles at intersections and increasing yielding rates. Finally, although we believe more research is needed, this study offered strong evidence that signage is very ineffective at increasing yielding rates. We hope that this research will prove useful for transportation planners and engineers who are looking for design methods to improve vehicle yielding rates and pedestrian safety. The implications of this are potentially safer streets for pedestrians & fewer fatalities.

The results of this study are also applicable to many other contexts of similar demographic & urban fabric, beyond Cambridge. The impact of our study highlights the limited effectiveness of signage and the pattern of non-compliance humans present in reaction to signage. Observing how physical attributes of street design are more successful in nudging drivers to yield suggests that cities need to reconsider their traffic flow strategies.

This is not limited to signage, but also traffic signals. There have been many studies & experiments in Europe (UK & Germany) for a shared concept of streets. They have found that by removing signals and directions, drivers inadvertently have to be more careful, they naturally slow down, and are more cautious for pedestrians.

Limitations Certainly, we were unable to isolate every variable. Some of the intersections in our study contain multiple design/information elements, and it is impossible to fully isolate only intersection design or information design. A more perfect study would involve test different treatments on the exact same intersection.

This study could have also benefited from more time to collect larger sample sizes and to study additional intersections. There were also additional factors that we believe could contribute to yielding rates that proved difficult to study, including poor weather, and whether taking a step into the intersection impacted driver yield rates. Due to safety concerns, evaluators could not move into the intersection until drivers came to a complete stop, though this does not mimic actual pedestrian behavior.

In addition, it was not possible to control for the impact of parked cars and the ensuing level of visibility of pedestrians attempting to cross the intersections. The specific parking situation at each intersection changed every day of data collections, and at certain intersections anecdotally we felt that cars parked close to the crosswalks prevented cars from fully seeing pedestrians waiting to cross, which may have affected yield rates at those intersections.

Finally, during the weekday data collection period in particular, the higher traffic count limited the completeness of the experiment because multiple cars would occasionally bunch up behind one car, and the decision of the first car to yield or not might have affected the decision of the cars behind them. When we were resetting the experiment, we would sometimes miss the opportunity to test several cars, because they had already seen the experimenter cross the crosswalk and we had to wait until they had cleared the intersection to continue the experiment.

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Extensions and Future Research There are a couple different axes on which this project could be expanded to lead to more robust results.

First of all, a bigger sample size is needed in order to draw more statistically robust results, both testing additional intersection design tactics and gathering more sample points for each of the intersections. Future research should also focus on a diverse set of crosswalk evaluators so that the study can better control for factors like height, gender and race.

Additionally, we think it would be useful to explore why reduced intersection width seems to be the primary factor in increasing yielding rates. This would most likely take the form of a behavioral experiment.

Explanations that we could explore include the visual narrowing effect. Such research would rely on behavioral science and psychology methods to study effect of road narrowing on vehicle speeds and tendency to yield.

Our experiment has shown that narrower intersection widths correlate with higher yield rates, but additional research could help clarify why this correlation exists.

Conclusion This project sought to determine whether different intersection design and information design interventions impact driver yielding behavior differently. After evaluating driver yield rates at seven intersections in Cambridge, MA, we did, in fact, find strong variations. Some of our most significant findings were aligned with prior research on the subject, including our finding that stop signs and tabletop street designs are effective strategies. Beyond those approaches, narrow street width was found to be the only statistically significant factor influencing yield rates. This study did not find signage to be an effective strategy. These findings also aligned with prior research and suggest that future research should explore techniques like road-width narrowing rather than continue to investigate interventions that are ignored by drivers, like signage. Though there were limitations in the scope of the data we collected, and limitations in sample sizes, this research may still be valuable to local officials. It demonstrates that interventions that focus on increasing awareness of a safety issue do not necessarily lead to safer outcomes, and it adds to the body of literature on street design and pedestrian safety. However, public officials are often limited in their ability control street design, even for the purpose of public safety. In speaking with the City of Cambridge, we learned that intersection design along Pearl and Brookline was a result of specific contextual details, like surrounding infrastructure, traffic volume, and the presence of trees. It was also heavily influenced by public requests for sign installations, despite the fact that the City staff knew this was an ineffective traffic calming technique. Local officials, like the City of Cambridge staff, must find solutions that meet budget constraints, do not cause negative externalities on other infrastructure, and meet community expectations. Adding curb bump-outs, installing stop signs, and building tabletops may not be implementable interventions for every intersection. However, officials should explore using new techniques to narrow street widths like paint and plastic bollards that do not require costly and permanent changes to the intersection (Seattle Right-of-Way Improvement Manua, 2017). In addition to improving street design, officials may want to focus on clarifying the driver yield law and increasing enforcement. The lack of clarity in the state law was the most concerning outcome of this study. Government officials disagree on the law’s interpretation, leading us to believe that drivers are also unclear on when and where they are required to stop for pedestrians. With clearer expectations of driver behavior, drivers might yield more predictably to pedestrians, leading to safer streets for everyone.

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REFERENCES Bennett, M. K., Manal, H., & Van Houten, R. (2014). A COMPARISON OF GATEWAY IN-STREET SIGN CONFIGURATION TO OTHER DRIVER PROMPTS TO INCREASE YIELDING TO PEDESTRIANS AT CROSSWALKS. Journal of Applied Behavior Analysis, 47(1), 3-15. Retrieved from http://search.proquest.com.ezp prod1.hul.harvard.edu/docview/1517530239?accountid=11311 Bertulis, T., & Dulaski, D. (2014). Driver Approach Speed and Its Impact on Driver Yielding to Pedestrian Behavior at Unsignalized Crosswalks. Transportation Research Record, 2464(2464), 46-51.

Boston . Transportation Department. (2013). Boston complete streets : Design guidelines. Boston, Mass.: Boston Transportation Dept.

Burden, D., Wallwork, M., Sides, K., Trias, R., & Rue, H. (1999). Street design guidelines for healthy neighborhoods (pp. 1-15).

Sacramento, Calif: Center for Livable Communities URL: http://onlinepubs.trb.org/Onlinepubs/circulars/ec019/Ec019_b1.pdf City of Cambridge. (2000). City of Cambridge Pedestrian Plan.

URL: https://www.cambridgema.gov/~/media/Files/CDD/Transportation/Pedestrian/ped_plan_2000.pdf?la=en City of Cambridge. (2017). Vision Zero Action Plan. URL: https://www.cambridgema.gov/~/media/Files/Traffic/visionzerodocuments/VisionZero_ActionPlan.pdf?la=en City of Cambridge. (2019). Vision Zero - Traffic, Parking & Transportation Department - City of Cambridge, Massachusetts [Government]. Retrieved May 7, 2019, from Traffic, Parking and Transportation Department website.

URL: https://www.cambridgema.gov/traffic/sustainabletransportation/visionzero City of Cambridge Police Department. (2017, May 25). CRASH TRENDS AND LOCATIONS: 2000 – 2016. Retrieved May 7, 2019.

URL: https://www.cambridgema.gov/~/media/Files/Traffic/Cambridge_CrashAnalysisReport_Final_05252017.pdf?la=en Dumbaugh, E., & Li, W. (2010). Designing for the Safety of Pedestrians, Cyclists, and Motorists in Urban Environments. Journal of the American Planning Association, 77(1), 69-88.

Ewing, R., & Bartholomew, K. (2013). Pedestrian & transit-oriented design.

URL: https://trid.trb.org/view/1250725 FHWA. (2014) Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed.

FHWA. Traffic Calming 29. Raised Intersection (Rep.). https://safety.fhwa.dot.gov/saferjourney1/library/countermeasures/29-30.htm Fruin, J. J. (1971). Pedestrian planning and design (No. 206 pp).

URL: https://trid.trb.org/view/114653 GHSA, & Retting, R. (2019). Pedestrian Traffic Fatalities by State: 2018 Preliminary Data( Rep.). https://www.ghsa.org/sites/default/files/2019-02/FINAL_Pedestrians19.pdf Goddard, Kahn, & Adkins. (2015). Racial bias in driver yielding behavior at crosswalks. Transportation Research Part F: Psychology and Behaviour, 33(C), 1-6.

Harkey, D. L., & Zegeer, C. V. (2004). PEDSAFE: Pedestrian safety guide and countermeasure selection system (No. FHWA-SA-04-003,).

Washington, DC: Federal Highway Administration.

URL: https://www.r2ctpo.org/wp-content/uploads/pedsafe_0-toc.pdf King, M. (n.d.). Calming New York City Intersections (Rep.). TRB Circular E-C019: Urban Street Symposium. http://onlinepubs.trb.org/Onlinepubs/circulars/ec019/Ec019_i3.pdf King, Michael R, Jon, A Carnegie, and Reid Ewing. "Pedestrian Safety through a Raised Median and Redesigned Intersections." Journal of the Transportation Research Board 1828 (1), 56-66, Transportation Research Board, Washington, DC. Perkins+Will Consultant Team. "Pedestrians at Multi-Modal Intersections." etter Market Street Existing Conditions & Best Practices, Part Two: Best Practices 36-58, City & County of San Francisco, San Francisco.

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Piff, P. K., Stancato, D. M., Cote, S., Mendoza-Denton, R., & Keltner, D. (2012). Higher social class predicts increased unethical behavior.

Proceedings of the National Academy of Sciences, 109(11), 4086–4091.

URL: https://doi.org/10.1073/pnas.1118373109 Retting, Richard A., Ferguson, Susan A., & McCartt, Anne T. (2003). A review of evidence-based traffic engineering measures designed to reduce pedestrian--motor vehicle crashes. The American Journal of Public Health, 93(9), 1456-1463.

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Turner, S., Fitzpatrick, K., Brewer, M., & Park, E. (2007). Motorist Yielding to Pedestrians at Unsignalized Intersections: Findings from a National Study on Improving Pedestrian Safety. Journal of the Transportation Research Board, 1982(1982), 1-12.

Turner, S., Fitzpatrick, K., Brewer, M., & Park, E. (2007). Motorist Yielding to Pedestrians at Unsignalized Intersections: Findings from a National Study on Improving Pedestrian Safety. Journal of the Transportation Research Board, 1982(1982), 1-12.

Van Houten, R., PhD, Hochmuth, J., Dixon, D., & McQuiston, C. (2018). SAFETY BENEFITS OF THE GATEWAY R1-6 TREATMENT: An examination of effects on drivers yielding to pedestrians, speed at crosswalks, and sign durability. Institute of Transportation Engineers.ITE Journal, 88(3), 31-39. Retrieved from http://search.proquest.com.ezpprod1.hul.harvard.edu/docview/2025760459?accountid=11311 Vision Zero Streets. (2019). Introduction. Retrieved May 7, 2019.

URL: https://www.visionzerostreets.org/ Vox, Road signs suck. (2017) What if we got rid of them all? Retrieved May 7, 2019. https://www.youtube.com/watch?v=VUbsFtLkGN8 Seattle Right-of-way Improvements Manual. (2017) Intersection Treatments. Retrieved May 18, 2019 https://streetsillustrated.seattle.gov/urban-design/adaptive-design/intersection-treatments/

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Appendix 1: Team Contributions As a team, we collectively came to an agreement on our project, scouted intersection locations and came to a determination on our final intersections. We then also came to a collective decision on the framework for our methodologies. We also all collectively contributed time and insight into the literature review section. Significantly, all four of us took an equal share of intersection testing. Finally, we all took part in producing copy and contributing critical thinking to our reports.

Mark Bennett: I initially created some basic maps to visualize our study locations and contributed the photos used in our final report and presentation. In conjunction with organizing and submitting documentation to the COUHE process, I wrote up the first robust methodology (with significant input from other teammates). I also set up what eventually became our shared data collection Google sheet, where I also calculated initial results from our first round of analysis.

Along with two other teammates, I participated in the city staff interview. With information and data from teammates, I put together our first interim report slideshow. Finally, I co-led the final statistical analysis, including regression analyses.

Avital Baral: I initially started organizing our project workflow through a Google Docs folder with the skeleton of our report. For the interim report, I compiled the literature review section and co-presented our findings, as well as provided writing/wording for several sections of the report. For the full report, I focused on the abstract, significantly updating the discussion section, and adding the Impacts and Limitations sections.

Mary Hannah Smith: In the first stage of the project, I developed the methodology section in original project proposal. For the interim report, I contributed to the literature review, wrote the project plan, and updated the methodology section.

Once we collected all our data, I explored different theories about it using data visualization techniques. I also participated in the City of Cambridge staff interview. Lastly, I wrote the conclusion and updated the literature review section in final report.

Ashutosh Singhal: I have been an active participant in group discussions – from the early conceptual frameworks, questioning the logic & scope of our experiment, to the experiment design itself. Beyond conducting the experiment on site, I have been involved in meeting with the city of Cambridge and compiling the information from the discussion.

Furthermore, I contributed to writing the abstract, hypothesis questions, literature review, early interpretations from the first experiment, producing the diagram explaining the experiment procedure on site, and also presenting on behalf of the group with Avital during the interim presentation.

Appendix 2: Interview Guide

1.

2.

3.

4.

5.

6.

7.

What is the reason behind the different signages at each intersection on Pearl & Brookline St? Is there a study or evidence that nudged the city of Cambridge to install two yield signs as opposed to one?

Why are there some intersections with no painted cross-walks?

Why are there curb extensions on only a few intersections?

Why is the tabletop cross-walk unique to a few intersections?

How does the state law influence the signage & street conditions?

When must a vehicle mandatorily yield and when not?

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Appendix 3: Technical Notes and Calculations Site Map

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Appendix 4: Description of Intersections in Study A. Painted Crosswalk with Two Ped Crossing Signs (Gateway) (Pearl at Allston)

B. Painted Crosswalk Only (Brookline at Franklin)

C. Painted Crosswalk with Stop Signs (Pearl at Putnam)

D. Painted Crosswalk with One Ped Crossing Sign, Overhead Flashing Light and Curb Bump Out (Brookline at Allston)

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E. Painted Crosswalk with One Ped Crossing Sign + State Law Explanation Sign (Brookline at Chestnut)

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Appendix 5: Observations WEEKEND: Intersection Pearl at Allston Brookline at Chestnut Brookline at Franklin

Treatment

Time

"Gateway" Two Ped Signs

18:05

10

12:30 Two Ped Signs + State Law

Only Painted Crosswalk

Brookline at Hamilton

One Ped Sign

Brookline at Allston

One Ped Sign + Blinking Light

Brookline at Erie Pearl and Putnam

WEEKDAY: Intersection Pearl at Allston Brookline at Chestnut Brookline at Franklin

One Ped Sign + Raised Intersection

Stop Signs

Cars Yielded 3 5

Yield Rate 17.60% 22.70%

20.50%

14:30 17:18

20 15

45 39

10 14

28.60% 36.80%

32.90%

17:30 11:45

16 25

36 23

16 5

44.40% 21.70%

35.60%

12:57

10

16:47

14

31 45

14 23

45.20% 51.10%

48.70%

13:32

16

17:18

21

23 47

15 21

65.20% 44.70%

51.40%

12:23

15

16:15

19

30 39

27 26

90% 66.70%

76.80%

18:45

17

13:00

14

22 17

20 17

100% 90.90%

94.90%

Total Cars 17 23

Cars Yielded 4 8

Yield Rate 23.53% 34.78%

30.00%

48 22

23 16

47.92% 72.73%

55.70%

14 25

3 1

21.43% 4.00%

10.30%

40 19

10 14

25.00% 73.68%

40.70%

10 18

10 18

100.00% 100.00%

100.00%

50 25

25 15

50.00% 60.00%

53.30%

45 21

30 16

66.67% 76.19%

69.70%

Time

"Gateway" Two Ped Signs

16:32

36

16:43

27

16:15

40

17:51

41

17:03

15

17:10

10

17:57

27

18:40

44

17:25

14

17:30

14

16:36

33

18:15

25

15:53

25

17:30

36

Two Ped Signs + State Law

Only Painted Crosswalk

One Ped Sign

Brookline at Allston

One Ped Sign + Blinking Light

Pearl and Putnam

12

Total Cars 17 22

Treatment

Brookline at Hamilton

Brookline at Erie

Normal Rate

One Ped Sign + Raised Intersection

Stop Signs

Normal Rate

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Appendix 6: Bivariate Regressions with seven and six intersections Full Set of Intersections

95% confidence

Dependent Variable: Yielding Rate

N=7

Variable

Unit

R Square

Significance

# Warning Signs

No. of signs

0.349998

0.16175885

Stop Sign

Present or no?

0.549761

0.05646987

State Law Sign

Present or no?

0.059886

0.59688416

Curb Bump

Present or no?

0.000427

0.9649319

Raised Int

Present or no?

0.127022

0.4326371

Blinking Light

Present or no?

0.000264

0.97240766

Width

Feet

0.080175

0.53834289

Traffic

No. cars/ 5 min.

0.000355

0.96803396

Without stop sign intersection

95% confidence

Dependent Variable: Yielding Rate

N=6

Variable

Unit

R Square

Significance

# Warning Signs

No. of signs

0.114597

0.51161447

State Law Sign

Present or no?

0.033525

0.72842327

Curb Bump

Present or no?

0.107059

0.52671768

Raised Int

Present or no?

0.5263

0.10270792

Blinking Light

Present or no?

0.044669

0.68769605

Width

Feet

0.278464

0.28192703

Traffic

No. cars/ 5 min.

0.390209

0.18487438

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Appendix 7: COUHES Approval

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