Any traffic engineer or transportation official would surely tell you that safety, if not the most important consideration, is truly a core priority. But embedded deeply in our federal transportation program is another guiding principle that stands in direct opposition to safety: “Cars need to always move fast and never slow down.” Whatever the stated priorities are, this hidden prerequisite makes every other goal a nearly impossible task—especially safety.

Slip lanes on roads and streets are emblematic of what it looks like in practice to sacrifice safety on the altar of speed, where this underlying goal of “keep cars moving fast at all times” runs counter to the goal of “keep everyone safe while moving from A to B”—even if you say that safety is important. If we truly prioritize safety, as T4America is suggesting in our second principle, we would never build a slip lane on a local street again. (Note: Slip lanes could be helpful in some rare cases for intersections designed for large buses or trucks to physically make a turn in the space allotted, or where the right turn is sharper than a 90 degree turn. But this is not why most exist.)

What are slip lanes and why do they exist?

It’s important to remember that slip lanes were created to solve one specific set of problems: vehicle speed and delay.

They were borne of the simple realization by traffic engineers that cars turning right—even on a green light—can produce dreaded congestion because slowing down to a safe turning speed can delay traffic traveling straight. So to solve this one problem, they started adding lanes that allow traffic to make right turns without being required to slow or come to a stop, often accompanied with an additional lane on the approach or the exit. Whether you live in a rural, urban or suburban area, this feature isn’t hard to find: they’re a regular feature in most environments that were designed and built with federal money and guidance over the last 50 years.