Bill may allow left turns on red at new interchanges

Unusual new "diverging diamond interchanges" that are appearing in Utah could allow a unique twist in traffic laws if a new bill passes the Legislature: the option of turning right or left at some stop lights.

The unique design of those interchanges has some drivers who hit red lights at them finding one-way traffic both to their right and left.

Their design eliminates left-turn signals by having traffic that would normally travel on the right-hand side of the road cross temporarily over to the left as it passes over or under another highway, and then it crosses back. From above, the traffic design looks like a helix.

While current law clearly allows turning right on a red light — if the traffic is clear, and no signals ban the turn — the law is murky about allowing left turns into one-way traffic to the left, Linda Hull, a lobbyist for the Utah Department of Transportation recently told the Utah Transportation Commission.

She said that has led to traffic back-ups at a diverging diamond off Interstate 15 at Thanksgiving Point in Lehi — sometimes backing traffic all the way up the ramp onto the freeway itself. She said engineers figure the situation could be improved if left turns on red were allowed there when traffic is clear.

UDOT persuaded Rep. Michael Kennedy, R-Alpine — whose constituents are served by the Thanksgiving Point interchange —  to introduce HB272 to allow such turns.

"With Adobe going in there, there's a lot more congestion depending on the time of day," Kennedy said. "I hope this would help reduce the back-ups."

His bill says that drivers "facing a steady red arrow signal may cautiously enter the intersection to turn left from a one-way street into a one-way street" if traffic is clear, and signs allows such turns there.

UDOT has another diverging diamond in West Valley City at the intersection of Bangerter Highway and SR-201. Hull said UDOT has not decided whether any left turns on red would be allowed there, and said backing there has not been as much of a problem.

UDOT is planning more diverging diamonds in the future because they help speed traffic by eliminating cycles for left-turn signals. "So this bill could be used for them," Hull said.