As a part of a safety and resurfacing project in 2020 and 2021, MoDOT made some significant updates to portions of Missouri Route 115 (Natural Bridge) in the city of St. Louis. As a part of this project, the department implemented a road diet on portions of the roadway, added roundabouts at three intersections and updated pedestrian crossings to include Rectangular Rapid Flashing Beacons and new crosswalk lighting.
When the work was complete, the department studied the corridor to see how effective those changes to the corridor were, and how much of an impact it had the pedestrians, cyclists, transit users and vehicles traveling the corridor. MoDOT looked at the three years prior to construction (2018-2020) and the three years after construction (2021-2023)
The results of the project, based on the study, were very effective in saving lives along the corridor.
How did this process start?
The crash rates on Missouri Route 115 (Natural Bridge), an arterial corridor in the northern portion of the city of St. Louis, were significantly higher than similar arterial routes in the St. Louis region. Leaders in the city of St. Louis reached out to MoDOT to discuss how they could improve roadway safety, while still allowing the corridor to operate as an arterial route. The corridor connected downtown St. Louis, local neighborhoods, and local destinations such as Fairground Park, Beaumont High School, and Julia Davis Public Library. Natural Bridge serves nine Metro Bus lines, one along the corridor and eight intersecting lines along other city routes.
In 2017, MoDOT, local city leaders, and local law enforcement conducted a road safety audit along the four-mile stretch of Natural Bridge in the city of St. Louis. The audit found that the entire corridor, which carries roughly 16,000 vehicles daily, had a crash rate higher than the state average for similar roadways, with some sections of the road being significantly higher. Three factors were common in these crashes along the corridor: people were speeding, people were improperly using lanes, and some people were not using crosswalks.
MoDOT discussed these issues with the community through focus groups and several public meetings. Members of the community shared their concerns and priorities for improving the safety of the roadway. MoDOT collaborated with the city’s public safety officials to implement a Travel Safe Zone along Natural Bridge and increase enforcement efforts. MoDOT created and shared several public service announcements with local media about the new Travel Safe Zone.
What are MoDOT’s responsibilities on the corridor?
Although Natural Bridge is city-owned, MoDOT has an agreement with the city to maintain the corridor from “curb to curb.” That means MoDOT maintains the driving surface, signing, striping, signals, and sweeping. The City of St. Louis is responsible for everything else - including sidewalks, lighting, roadway access, drainage, permitting, landscaping, and other maintenance issues. MoDOT and the City regularly coordinate on all updates along the corridor.
What was built on Natural Bridge?
From the discussions with the community, MoDOT developed plans to update Route 115 (Natural Bridge) from the city limits to Interstate 70. Prior to the work, the typical roadway consisted of a four-lane wide section with space for parking and/or a center turn lane. Traffic was primarily controlled by signals and pedestrians had to cross the entire width of the roadway with no median or pedestrian refuge islands.
In August 2020, MoDOT started the project, which included the following roadway changes:
- Implementing a roadway reconfiguration (lane reduction) between Shreve and Parnell/Salisbury with raised concrete center medians to divide traffic and fill space. Drivers now have one lane in each direction, with left turn lanes at cross streets. The remainder of the roadway has a median, with designated places for pedestrians to cross safely.
- Converting signalized intersections to roundabouts at Goodfellow, Vandeventer and the Salisbury/Parnell intersections.
- Incorporating new mid-block crosswalks with rectangular rapid flashing beacons (RRFBs) and additional crosswalk lighting in several locations along the corridor.
The project finished in late 2021.
Natural Bridge is a commuter corridor into the city. How do these changes benefit commuters?
In the years leading up to the project, Natural Bridge had a higher crash rate than similar roads with the same amount of traffic. Many of those crashes involved pedestrians. During a safety analysis of the roadway, three factors were common in these crashes along the corridor: people were speeding, people were using lanes improperly, and some people were not using crosswalks.
We had several discussions with a select group of business owners, residents, and individuals who work and travel through this area. During our discussions, the community stressed that their safety, and the safety of the people who live, shop, and work along Natural Bridge are paramount. These improvements will keep traffic flowing along the corridor, and will slow down traffic, reduce improper lane use, and offer more locations for pedestrians to safely cross the street. Every engineering decision must balance the needs of different users, but what benefits one group of users may feel have a reciprocal impact on another group of users. The department’s goal is to listen to what the community desires and do what we can to best meet the needs and wants of all roadway users. In this case, the top priority for those who live and work along Natural Bridge is slowing down traffic to the posted speed limits and making it safer to travel on, and cross, the roadway. As drivers relearn the new traffic patterns, and as traffic adjusts to the new layout, future adjustments may be considered, as long as they continue to meet the communities’ desires.
Areas of improvement: due to public interest, different improvements were implemented in three primary areas:
- Western zone: Darby Street to Siemers Lane
- Central zone: Siemers Lane to Shreve Avenue
- Eastern zone: Shreve Avenue to Parnell Street
The roadway was studied for the three years after the project was finished to determine how the improvements affected safety and traffic for both vehicles and pedestrians. Daily traffic levels across the St. Louis region trended lower between 2021 and 2023. Natural Bridge saw a similar trend in the sections with and without the roadway reconfiguration.
Various safety improvements (including roundabouts and roadway reconfigurations) were included in the areas west of Siemers Lane and east of Shreve Avenue; there were minimal improvements (updated crosswalks and signal plates) between Siemers and Shreve.
Changes on Route 115 (Natural Bridge) due to safety improvements
Information gathered from studying the three years prior to construction (2018-2020) and three years after construction (2021-2023). At the time of the study's completion, 2024 information was not available.
Information provided is gathered from a traffic study of the corridor for three years prior to construction (2018-2020) and three years post-construction (2021-2023)
Fatal and injury crashes decreased significantly on Route 115
In the study timeframe, fatal and injury crashes decreased 35 percent on Route 115. Fatal and injury crash rates increased roughly 5 percent on similar corridors in the same period.
Fatal and injury crashes decreased more in the reconfigured areas
Serious injury crashes in the areas between Darby Street and Clara Avenue and Marcus Avenue and Parnell Street (that were reconfigured)decreased by 35 percent. Fatal crashes in the same area were reduced by 61 percent.
Serious injury crashes in the area between Clara Avenue and Marcus Avenue (that were not reconfigured) increased by 93 percent. Fatal crashes in the same area increased by 54 percent.
Traffic volumes decreased slightly around the region
Although traffic volumes did decrease in all areas across the corridor, they were similar to decreases on other similar corridors during that time. It appears that drivers did not change their routes to avoid using the areas with the roadway reconfiguration.
Traffic did not take alternate routes around the modified areas
MoDOT evaluated parallel arterial routes, like Route 180 ( Dr. Martin Luther King Dr/St. Charles Rock Road). Traffic levels did not increase are similar parallel arterial routes.
Traffic delays remained unchanged along the corridors after the improvements
Most intersections either stayed the same or had a slight improvement in how well the intersection functioned. One intersection in the morning (Taylor) was slightly worse, as was one intersection in the evening (Marcus). The greatest reductions in delay were at the intersections where signals were replaced by roundabouts (roughly 20 seconds in the morning and 15 seconds in the afternoon).
Travel times were not significantly impacted
For the most part, travel times decreased -- for the most part about half a minute of difference. Travel times in the evening increased slightly -- less than half a minute.
Vehicle speeds reduced along the corridor
The speed limit on the corridor is 35 mph. The roadway reconfiguration reduced vehicles traveling over 65 mph from 1.5 percent to 0.2 percent -- a drop of 155 fewer cars traveling over 60 miles per hour per day. Average vehicle speeds reduced up to 7 miles per hour.
Lanes are wide enough for emergency vehicles and plows
In the modified areas, lanes are at least 14 feet from curb to curb, wide enough for plows to get through and wide enough for emergency vehicles.