PHILADELPHIA (KYW Newsradio) — PennDOT sees “encouraging signs” in the first round of data from its Variable Speed Limit (VSL) system along the Schuylkill Expressway.
Engineers stress that, while more study is needed, a PennDOT analysis of the system’s first six months shows a downward trend in highway crashes and a slight improvement in travel times.
In May 2021, 72 VSL signs were activated along the 14-mile stretch of I-76 between Route 202 and Route 1. The changing speed limit signs are designed to slow traffic ahead of congested areas, to reduce the risk of rear-end collisions and improve traffic flow.
According to a PennDOT data analysis from June to December 2021, the number of overall crashes was 10% higher than the five-year average from 2015 to 2019.
Full PennDOT study on variable speed limits
However, monthly crash totals steadily decreased and, by December, were below the five-year average, said Dave Adams, PennDOT acting senior manager for traffic operations.
“Montgomery County is the largest section of I-76,” Adams said. “And month by month in the last half of 2021, we’ve been seeing crashes decrease month by month from June through December.”
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In the one-mile stretch of the VSL in Philadelphia, crashes rose to nine in December 2021 compared to the five-year average of five crashes.
According to PennDOT’s report corridor traffic conditions may be “contributing factors” in the increase. Adams pointed to the need for more data.
Overall, the average end-to-end eastbound travel times were reduced by a minute and a half in the morning, and westbound, the time savings was about 30 seconds.
Reverse commute times saw a particular bump.
Average end-to-end travel times improved by four minutes westbound in the morning and five minutes eastbound in the evening. Adams said that improvement may indicate that drivers were becoming more familiar with the variable signs.
“So far, we’ve been seeing reductions in travel time, which is a good thing. It shows that the system has been paying off.”
While Adams noted improvements, some motorists who drive the Schuylkill Expressway question the effectiveness of the VSL system.
“I understand if there’s an obstruction and it’s necessary,” said Drew Christiano of Devon. “But a lot of the times, it has been inexplicable.”
When asked if he obeyed the VSL signs, Christiano said, “If the road is clear, I don’t. They kind of act like a traffic warning. Like, if I see the speed limit’s lower, I’m like, ‘okay, it’s probably slower up ahead,’ But if it’s open and the speed limit’s lower, no.”
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