(Ed. Note: With the forthcoming release of the LADOT Bike Program SLM (Shared Lane Marking) Study, the LADOT Bike Blog would like to take you back to the summer of 2010 and share with you the methodology of our Sharrow study. Confused? Check out our Sharrows 101 post or our Sharrows Page.)
Over three weeks in late May and early June of 2010, LADOT Bike Blog took part in pre-installation studies for the LADOT Shared Lane Marking (Sharrows) Study. The study documented the interactions between drivers and bicyclists when a bicyclist traveled at the position where Sharrows would later be installed. At the end of the summer, LADOT Bike Blog again took part in studying the interactions between drivers and bicyclists, this time with Sharrows in place. It all culminates with the release in the next few days of the LADOT Bicycle Program SLM report.
While the LADOT Bike Blog will have another write-up on the results of the report (and what it means for Los Angeles’ streets), we first wanted to give you a look at the goals, the methods, and the standards we used for the Sharrow study.
We don’t just want Sharrows, we want Sharrows the right way. We’re happy to give you a look at how we got there.
LADOT’s Sharrows study builds off of the work of the City of San Francisco, whose pilot project led to the 2005 adoption of SLMs in the CA MUTCD (California Manual of Uniform Traffic Control Devices). But rather than a wholesale adoption of San Francisco’s work, the LADOT Bike Program wanted to look at the effect of Sharrows on streets with different roadway designs (called “geometrics” by transportation engineers), traffic volumes, and roadway speeds. Taking a closer look at the effects of Sharrows on different types of streets in LA helps give us an idea of where Sharrows will have the greatest safety effect for bicyclists and drivers alike.
After field checking dozens of potential locations, the Bike Program staff chose six sites for pre-SLM studies: Fountain Avenue, 4th Street, Reseda Boulevard, Adams Boulevard, Westholme Avenue, and Abbot Kinney Boulevard. In late summer, one month after installation, Bike Program staff came back to measure for any changes in motorist behavior towards bicyclists. Using the wealth of information garnered from these before-and-after studies, LADOT now has a solid statistical rationale for implementation of Sharrows across the City.
The SLM pilot project locations range between just under one mile to just over three miles. Each site met a certain criteria: the street is either a Class III Bike Route, is near to pre-existing bike infrastructure, or is used regularly by bicyclists. The locations chosen also have unique street typologies, allowing us to study driver behavior on streets with different geometric conditions. These are the conditions of each study site within the pilot project areas:
- Fountain Avenue is classified as a “Secondary Highway”. It’s a one lane each direction street with few signals and a dash yellow center line between traffic. The study site’s curb lane width (the distance from the curb to the end of the travel lane adjacent to street parking) of 18-21 feet, has high parking demand (without restrictions), and has a posted speed limit of 30 mph. Some areas of Fountain, like just west of Vermont, have a significantly broader curb lane width.
- 4th Street is classified as a “Collector Street”. It is also a one lane each direction street, but has many stop signs and has no striping between lanes of traffic. Its study site also has a 20 foot curb lane width, but the parking demand is medium-to-high and a posted speed limit of 25 mph.
- Reseda Boulevard is classified as a “Major Highway – Class II”. It is a two lane each direction, signalized thoroughfare. The curb lane width for the study site vary from 21 to 22 feet. Parking is metered, parking demand is high, and there is a posted speed limit of 35 mph.
- Adams Boulveard is classified as a “Scenic Major Highway – Class I”. It is a 4 lane, high volume, signalized thoroughfare with a study site curb lane width of 19 to 20 feet. Parking demand is medium-to-high with no parking restrictions and a posted speed limit of 35 mph.
- Westholme Avenue is classified as a “Collector Street”. It is a 2 lane road with study site curb lane widths of 17.5 feet – the narrowest in the study. Parking demand is high, with 2-hour preferred parking restrictions on the street. The speed limit is posted at 25 mph.
- Abbot Kinney Boulevard is classified as a “Secondary Highway”. It is a 2 lane road, with a two-way left turn lane and turn pockets between them. It has study site curb length widths of 21.5 feet, has high parking demand with 2 hour parking restrictions, and a posted speed limit of 30 mph.
Volunteer bike riders for the study were organized by the Los Angeles County Bicycle Coalition(LACBC), who did a wonderful job at making sure riders were on time and prepared. Riders were required to have a standard street-legal bike, a helmet, and were supplied with computers by the LACBC to track their speed. LADOT Bike Blog and another Bike Program coordinator, Oliver Hou, also rode in the study. Riders were sent out in front of a platoon of drivers and, after finishing, would loop back around the block to cue up before being sent out again, and again, and again….
Bike Program staff supplied riders with water, Clif Bars, bagels, orange juice, and free LADOT Bike Program swag.
The key numbers for the study are 100, 12, and 12.
- The sample size for each phase of the study was 100 interactions between drivers and bicyclists. Each study had a morning rush-hour phase, from 8:00 to 10:00, and an afternoon rush-hour phase, from 4:00 to 6:00, for a total of 200 interactions a day. 100 interactions was the most that could be hoped for within each 2 hour block, and the study would occasionally run past the time allotted in order to hit that 100 interaction goal.
- Bike Program staff positioned two vans at each end of the route to record interactions. Routes were kept between one quarter to one third mile so staff documenting the interactions in the vans had a clear view. In addition to video cameras in each van, Bikeways engineers did manual counts of interactions between drivers and bicyclists.
- Bike Program staff looked only for samples where a driver interacted with a bicyclist; rides would occasionally be thrown out of the study when a driver turned off the street before an interaction took place. Staff documented drivers’ interactions with bicyclists at a Sharrows’ distance (12′) from the curb, leading to a wide range of reactions: Some drivers made a broad, safe pass around the bicyclist; some merged halfway into the next lane while passing; some tried to squeeze through the lane regardless of the biyclists’ position; some waited in the right lane behind the bicyclist. Some drivers were courteous while other drivers were very aggressive and angry. LADOT Bike Blog got his fair share of honks and yelled epithets while riding for the study (this was before the adoption of the Bicyclist Anti-Harassment Ordinance).
- 12 feet from the curb. The center of the Sharrows in this study are placed 12 feet from the curb, ostensibly the location to ride in the street to avoid being doored. Though the minimum requirement for Sharrows in the CA MUTCD is 11 feet, Bike Program staff came to the conclusion that 11 feet was still too close to parked cars. The 11 foot standard in the CAMUTCD assumes a 7 foot parking lane, and many parking lanes in LA are, in fact, 8 feet wide.
- To show where we wanted study volunteers to ride in the street before installation, and to get an approximate idea of how much passing room each driver took, Bike Program staff painted a series of orange dots along the study route. These dots helped position bicyclists in the before study and helped with video file analysis afterward. The dots started at 10 feet from the curb and were spaced every 2 feet. The bicyclists in the study rode through the center of the second dot to stay at a consistent 12 feet.
- The study needed to keep distances (12 feet) constant across pilot project sites to have comparable data. While some streets had very wide travel lanes (like Reseda), going further than twelve feet would place Sharrows to the left of center in the narrowest pilot site (sections of Westholme Ave have a 17.5 foot curb lane width).
- Bike Program staff wanted to control as many variables a possible, including bicycle speed, so different interactions between bicyclists and drivers would be solely dictated by the drivers’ actions. 12 mph might seem a little slow for some riders (and a little fast for others), but staff wanted to create a common denominator. 12 mph is the average cruising speed on a busy street. The required bicycle computers on each bike allowed riders to make sure their speed stayed at 12 mph.
Armed with hours of video and stacks of manually entered checklists, LADOT Bike Program staff has spent months synthesizing and analyzing the thousands of interactions recorded in the pre-and-post installation studies. In a few days, LADOT will release our report on the results of the study. LA has the chance to set a precedent for American cities in future implementation of SLM, as no other city has engaged in such a finely grained study. When the report goes public, LADOT Bike Blog will be there to provide further analysis of its recommendations.