You can legally drive 70 mph on I-90 between Elgin and Mount Prospect now

Motorists on I-90 now have about 24 additional miles to be legally lead-footed.

The stretch of tollway between Mount Prospect Road and Randall Road in Elgin had the speed limit increased to 70 mph late Tuesday. For buses, the speed limit will be 65 mph, and for commercial trucks the new limit will be 60 mph.

The move came after months of discussion and then approval by the tollway board, the Illinois Department of Transportation and the state legislature's Joint Commission on Administrative Rules.

Since a yearslong widening project was completed recently on this section of the Jane Addams Tollway, drivers have routinely ignored the posted 55 mph limits, authorities admitted.

Tollway officials said studies backed up the board's decision to increase the speed limit.

“(The) study ... reviewed factors that included the volume of traffic, traffic congestion, the frequency of access points like interchanges and oases, and the prevailing speed. That study determined it was appropriate to raise speed limits for that segment of I-90,” said tollway spokesman Dan Rozek.

The new limit for the 24-mile stretch now matches that of the remainder of I-90 between Elgin and the Wisconsin border.

Traffic safety experts said the increased speed limit could have both beneficial and dangerous side effects.

“Now that everyone should be doing 70, there's not as much difference between speeds on the road,” said Charles Roberts Jr., a Rochelle-based traffic engineering consultant. “Increased speed tends to reduce reaction time, but on the tollway, that's usually not much of a problem.”

However, other traffic engineers worried the increase in speed would lead to an increase not only in the number of crashes but also in their severity.

“During the gas crisis of the 1980s when the government reduced speed limits, there was a huge side effect of fewer accidents, and the ones there were, they were less severe,” said Gary Hutter, a transportation safety expert at Glenview-based Meridian Engineering & Technology Inc. “When the speed limit is 55, people are typically going 65. When it's 70, they're going 80, and when they want to pass someone it's even faster.”

Hutter also noted that hydroplaning on wet surfaces becomes a bigger concern for vehicles at higher speeds.

“Less reaction time, higher speeds, greater likelihood of hydroplaning,” he said, “all those things conspire to move you into a place where there's more likely to be accidents.”

Illinois State Police did not immediately respond to calls and emails asking whether they would beef up patrols during the transition to keep drivers in check.