WSP Uses Highway Capacity Software to Evaluate Congestion Issues on Route 17

Traffic is a constant problem on New York State Route 17, and if you have driven along this route during rush hours or headed out of town for the weekend, surely, you’ve been held back by the crawling traffic, or worse yet, have found yourself coming to a complete stop.

Recognizing the need for a deeper understanding of these recurring delays, the New York State Department of Transportation (NYSDOT) launched the NYS Route 17 Mobility and Access Improvements Project. The goal: identify the causes of congestion and evaluate solutions that can improve traffic flow both now and in the future.

To support this effort, the leading consultant WSP led a comprehensive traffic analysis using the Highway Capacity Software (HCS), developed by the University of Florida’s McTrans Center. McTrans also played a key role as a subconsultant, providing expert review and validation of the modeling process to ensure reliable results.

The traffic analysis study examined a 30-mile-long corridor in Orange and Sullivan counties, New York, from US Route 209 to Interstate 87. This is where Route 17 is located and experiences recurring congestion during peak periods on weekdays and weekends. This corridor contains closely spaced ramps and short weaving sections – elements that can affect how traffic behaves.

To determine whether these elements are contributing to reduced speeds, delays, and recurrent congestion, WSP used the HCS Freeway Facilities module to simulate traffic operations along the mainline NYS Route 17 corridor, including potential bottleneck locations such as merge, diverge, and weaving areas.

Travel times were collected along the route during peak travel periods, including the morning and evening commutes to work, and on Friday and Sunday afternoons. The data was collected throughout 2023 and included speed and traffic volumes. The HCS analysis showed that congestion on Route 17 happens at multiple sections of the corridor during peak travel periods.
The traffic study also looked beyond the results for existing 2023 conditions. The corridor was evaluated with HCS for its performance in two future design years:

• 2030, when congestion becomes more frequent during peak periods.
• 2050, when large portions of the corridor are projected to operate at Level of Service (LOS) D, E, or F.

The findings from these models indicate that the existing configuration cannot reliably accommodate future traffic demand. To alleviate congestion and improve travel times, three design concepts were evaluated:

• Concept 1: Targeted Operational Improvements
  This concept focuses on auxiliary lanes and collector distributor (C D) roads at critical locations to mitigate ramp turbulence and address localized bottlenecks.
• Concept 2: Peak Period Shoulder Lane with Select Third Lanes
  This alternative introduces part time shoulder running during peak periods, combined with limited full time lane additions and interchange improvements.
• Concept 3: Continuous Third General Purpose Lane
  This alternative adds a continuous third lane through the most congested segment, along with C D roads and interchange reconfiguration to improve both capacity and safety.

As a subconsultant, McTrans provided a detailed review of the HCS models to ensure alignment with Highway Capacity Manual (HCM) guidelines and consistency with observed field conditions. Key contributions included:
Advising on appropriate HCM methodologies for freeway facility analyses;

• Reviewing model inputs, including roadway geometry and traffic data
• Supporting calibration efforts using Capacity and Speed
• Adjustment factors, to ensure that HCS travel times reflect field measurements and the model bottlenecks represent congestion observed in the field.
• Assisting with HCS features, such as CSV import, to streamline the input of large amounts of data for different alternatives.

Fabio Sasahara, Ph.D., McTrans’s traffic engineering lead who worked on the project as a subconsultant, said reviewing the models was an important part of ensuring the analysis reflected real-world conditions.

Both the traffic analysis and the model review provided a better understanding of how Route 17 currently operates. They demonstrate how software such as HCS can help solve real-world challenges and support decisions that make a difference in our communities.

The complete project documentation for the Project Scoping Report, including the traffic study report, is available at this link.