A little R&R: Optimizing intersection improvements with rail crossing and roundabout solutions

Windsor River Road / Windsor Road Intersection Improvements and Multi-Use Path Connector Project
GHD Town of Windsor Roundabout

At a glance

There are a limited number of roundabout installations in the USA with at-grade railroad crossings within the center circle. Fewer still are installed on railroads that transport both freight and passengers. 

The Windsor River Road / Windsor Road intersection improvement project, included an at-grade rail crossing within a roundabout, which entails an intricate design and many technical details to ensure a safe and coordinated multi-modal vehicular flow. 

GHD's roundabout solution delivers benefits to the Town of Windsor community, including enhanced multi-modal connectivity and a better sense of place and gateway into the Town Green area.


The Town of Windsor looked to improve the intersection of Windsor River Road and Windsor Road to simplify right-of-way transfers from vehicle to rail activities. By doing this, they hoped to create better pedestrian access, reduce conflict points, and allow better flow for all modes of transportation. The Town aimed to create a better sense of place and gateway into their Town Green area.

The challenge

The major challenge was to make this intersection safer and more efficient for all modes of transportation since the original intersection design was not conducive to pedestrian or bicycle traffic, and data showed the collision rate of vehicles at the intersection was higher than the statewide average for a four-way signalized intersection. The conversion of a signalized intersection to a roundabout is estimated to reduce the number of injury collisions by 75%. 

However, current regulations and guidance express operational concerns with vehicle and transit interactions at railroads. These include queueing at the roundabout entry and extending through the rail crossing, concerns for pedestrian safety, issues with parking on an exit, and other factors that can create queues onto the rail crossing. 

The project is comprised of replacing a four-way signalized intersection with a roundabout that needed to include at-grade rail crossing safety devices, pedestrian crossing safety improvements, and a 760 linear-foot segment of the Class I Sonoma-Marin Area Rail Transit (SMART) multi-use path alongside the rail line. 

Roundabouts are still uncommon in the United States, even without the rail component, and not all designs effectively achieve operational goals for an intersection. Designers' expertise is key for passive control of multi-modal traffic: rail lines intersecting through vehicle, bus, pedestrian, and bicycle flow. 

Our response

We provided project planning, public outreach, permitting, grant assistance, design (including right-of-way, survey, geotechnical evaluation, and rail design,) and engineering services during construction.

During the design phase, our traffic modeling demonstrated that converting from a standard intersection to a roundabout would reduce peak-hour queuing while recovering faster when trains are present and the railroad warning devices are activated. 

The team showed that the roundabout improved operations during normal operations and just after the deactivation of the railroad crossing gate arms. The intersection queuing when the railroad safety gates are down at both the signalized and roundabout intersections was analyzed using simulation software, revealing normal queuing issues are made worse in both cases when the gates are down and the roundabout option restored the queues to the pre-train “normal” faster.

The project required coordination and approvals for the at-grade crossing modification by SMART, Federal Rail Administration and the California Public Utilities Commission.

The impact

The roundabout solution delivers benefits to the community, including enhanced multi-modal connectivity and a better sense of place and gateway into the Town Green area. As compared to the signalized option, the increased traffic queues clear faster with the roundabout option, given the benefit of faster recovery and allowance of certain right-turn movements being allowed to take place while the railroad crossing equipment has been activated. This provides clear advantages of a circular intersection, which enhances a sense of place, including upgrades to all modes of travel, whether by motor vehicle, walking, bicycling, taking the bus, or passenger train.

Our design created infrastructure that residents and businesses can use and take pride in while helping to establish Windsor’s identity for visitors. The roundabout provides a unique gateway into the Windsor Town Green area, Sonoma County Transit Hub and future SMART Windsor Station.

The Windsor River Road / Windsor Road intersection improvement project was recognized by ACEC California, receiving the 2024 Honor Award for the Transportation category.