Using Replica’s Road Closure Scenario Tool to Forecast the Impact of Construction in San Ramon, California

In order to install a bike and pedestrian overcrossing, the City of San Ramon will need to stop traffic on Bollinger Canyon Road for nine days, forcing roughly 40,000 trips to be rerouted each day. As the winner of Replica’s Road Closure Scenario contest, the City received a free road closure Scenario to better understand the potential impact of rerouting these 40,000 trips and inform appropriate diversion plans and signal modifications given the forecasted traffic impacts. We’re sharing the results of that scenario — which took less than 1 week from start to finish — below.

Published on
May 6, 2024

San Ramon is a city of more than 85,000 people in Contra Costa County, California. Bollinger Canyon Road, an east-west arterial, is one of the busiest roads in the city, as it bisects Interstate 680 in the City’s downtown business district. In order to build a bike and pedestrian overcrossing to improve pedestrian safety, the road, just under half a mile east of the on-ramp to I-680, will need to be closed for 9 days.

Understanding Existing Conditions. To start, we used Replica Places data to understand who utilizes the to-be-closed portion of the road. On a typical weekday, roughly 40,000 trips traverse Bollinger Canyon Road between Camino Ramon and Alcosta Boulevard.

  • These trips are overwhelmingly private automobiles. Just 1% of trips are commercial freight vehicles. 
  • Trips are more likely to be for the purposes of shopping, running errands or visiting a restaurant (combined 39%) than they are to be headed to work (19%).
  • Because the trips are more likely to be for discretionary travel than home-to-work trips, it’s not surprising that the time-of-day distribution for trips that utilize these segments shows more of a PM than AM peak.
Start time distribution for all trips that utilize the to-be-closed portion of the road.
  • 98% of trips are longer than 5 minutes, and 95% of trips are longer than 2 miles, making it unlikely that travelers could easily switch to walking or biking trips when the road is closed to cars.

Running the Scenario. To forecast the impact of the road closure, we simulated a full 24 hours worth of weekday traffic for Contra Costa County and the surrounding area — a zone with a population of more than four million people.

In collaboration with the City of San Ramon, we identified the network links to close. While San Ramon shared their traffic handling detour plans with us, we did not use this information as input to the scenario. In this way, the scenario run serves as a new perspective to study the impact of the road closure, rather than biasing toward any existing assumption.

“Being able to visualize what paths drivers might take with the full closure was mostly expected, but the road closure scenario also exposed a few surprises. The depth of the information used in the analysis will help us prepare a better outreach strategy for the future closure.” - Deborah Fehr, City of San Ramon

What We Found. The result of the scenario analysis can be explored in the embedded map below. You can hover over any link to see the change in estimated daily traffic. 

Here are our biggest takeaways from the result:

  1. The combination of the relatively minor scale of the closure, the non-permanent nature of the change, and the lack of easy alternative mode choices (particularly public transit) mean that there is little trip or mode substitution due to the closure. There is negligible change in total trips, mode split or vehicle miles traveled; rather, people who traversed Bollinger Canyon Road to get to their destination continue to take the same trip via alternative routing.

  2. The majority of trips are rerouted to Crow Canyon road, an exit further north on I-680. We estimate a 23% increase in traffic on Crow Canyon road eastbound, from those exiting the freeway, and a 15% increase in traffic westbound, from those adjusting their typical route to enter the freeway here rather than at Bollinger Canyon.

  3. While the majority of the rerouted trips go north, the downstream impact of the closure seems to be more acute on smaller east-west roads south of the closure. Many local roads here have projected volume increases of more than 30%, with some expected to have 60% more traffic than usual.

  4. The scenario also suggests some people may try to circumvent the closure by driving through the Executive Parkway and the Bishop Ranch 15 Parking Lot immediately north of the closure.

    By identifying this hot spot, the scenario can help San Ramon prioritize mitigation strategies (like cones, closures, or traffic officer placement) in an area that otherwise could end up being one of the more dangerous downstream impacts of the closure — increased through traffic in pedestrian heavy parking lots.
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