Anti-climbers worked only at fairly low speeds. Almost all streetcars were eqipped with anti-climbers. They rarely telescoped when they colided. Flimsy end platforms frequently collapsed but that's a different story.

The Key System-Sacramento Northern car collision of 1924 and the Napa Valley collision of 1913 resulted in telescoping and loss of life in spite of anti-climbers.

At some time, possibly the 1930's, the ICC ruled that passenger car floor heights must be the same as freight cars to minimize the possibility of telescoping. If you compare photos of interurban cars in the 1920's with the same cars in the 1930's, you can see that they have been raised. Look at the clearance between the top of the wheels and the bottom of the car body. Often steel spacers about 4 inches thick had been placed between the body and the trucks. Sometime steps had been modified to put the bottom step closer to the ground after the body was raised.

This regulation supposedly caused the Key System Bay Bridge Units to have high floors. It prevented Key from buying modern low-floor cars that were beginning to be used on other transit systems.