PURPOSE AND NEED
Purpose:
The purpose of the Nice Bridge Improvement Project is to upgrade the bridge design to conform with existing roadway approaches on both the Maryland and Virginia sides of the Potomac River; to improve traffic operations and safety across the bridge; and to reduce traffic impacts during anticipated significant bridge maintenance and rehabilitation.
Need:
This project is needed to address current conditions at the Nice Bridge that impact traffic operations and safety. These conditions are related to the following:
- Roadway Design Features.
- Traffic Operations and Safety.
- Bridge Maintenance.
- Roadway Design Features
Median separation:
The approach roadways to the Nice Bridge include a varying width median that provides a physical separation of vehicles traveling in opposite directions. The Nice Bridge has no physical lane separation between vehicles traveling in opposite directions. This reduction in travel lanes impacts traffic operations, as vehicles in the two lanes on the approach roadways merge to one lane to cross the bridge.
Number of travel lanes:
The US 301 approach roadways consist of four lanes with two lanes of travel in each direction. The Nice Bridge has one lane of travel in each direction. This reduction in travel lanes impacts traffic operations as vehicles in the two lanes on the approach roadways merge to one lane to cross the bridge, and the capacity of the bridge is reduced as compared to the approach roadways.
Width of travel lanes:
The approach roadways of US 301 to the Nice Bridge consist of 12-foot wide travel lanes in each direction. The Nice Bridge travel lanes are 11 feet wide. The narrower travel lanes on the bridge reduce its capacity, as 12-foot travel lanes are typically desired and lessen the frequency of bridge closures for wide-load crossings.
Available shoulder:
The US 301 approach roadways include a 10-foot wide outside shoulder in each direction; however, the travel lanes on the Nice Bridge have only one-foot outside buffers to the bridge parapet. Bridge capacity is reduced as a result of this lack of shoulder area. The existing one-foot outside buffer provides inadequate area for disabled vehicles to pull out of the traffic, for emergency vehicles to access incidents on the bridge, and for minor repair or maintenance activities to be performed without closing one direction of travel on the bridge. There is also a lack of a nearby waiting area for southbound wide-loads.
Vertical grade:
The maximum vertical grade on the southern and northern approach roadways of US 301 to the Nice Bridge are 2.6 percent and 1.0 percent, respectively. Vertical grades on the bridge structure reach 3.75 percent, making it difficult for heavy trucks to maintain the posted speed limit reducing the average travel speeds and the capacity of the bridge. Trucks account for approximately nine percent of total traffic on an average summer weekend day and up to 20 percent on an average weekday. This weekday average exceeds the Maryland statewide average of nearly 15 percent truck traffic on other four-lane rural principle arterials.
Traffic Operations and Safety
Traffic Operations:
A total of 6.4 million vehicles used the Nice Bridge in 2005, and daily trips across the bridge averaged nearly 26,000 on summer weekend days and 18,800 on weekdays in 2005. Traffic operation analysis indicates that the traffic volume in the existing peak hours on the bridge approaches the capacity of the roadway. Normal (non-holiday) weekend vehicle queues have been reported to extend up to 0.25 miles along US 301, while on major holiday weekends, queues have been reported to extend approximately four miles along US 301 at the bridge.
Safety:
Crash data for the Nice Bridge study area was analyzed for the period from January 1999 to October 2002. During the study period, a total of 38 crashes occurred in the study area, which equates to 67.0 crashes per 100 million vehicle miles of travel (VMT). This rate is below the Maryland statewide average for similar roadways, which is 109.5 crashes per 100 million VMT. The type of crash most often experienced in the study area is rear-end collision. Single lanes in each direction, congestion, and lack of shoulder on the bridge contribute to rear-end crashes. The majority (80 percent) of these crashes occurred on the bridge structure. There was also a high correlation between the roadway condition (wet, icy conditions) and crash occurrence. Approximately 32 percent of the crashes involved trucks, resulting in a truck crash rate of 21.2 crashes per 100 million VMT, the Maryland statewide average rate of 8.7 crashes per 100 million VMT for similar roadways. Updated safety data will be provided as the project proceeds.
Bridge Maintenance:
Based on the current condition of the bridge deck and the projected increase in traffic volumes, it is anticipated the deck will require rehabilitation in approximately year 2025. Depending on the type and method of construction, the rehabilitation could require long-term single lane closures or complete nighttime bridge closures as was done during the last deck rehabilitation in 1985. Due to the lack of nearby alternate routes and the bridge's single lane capacity in each direction, substantial travel time delays could result during rehabilitation.
