The claim the roundabouts will “reduce collision rates” on the TAMC Project Fact Sheet is also questionable since the only collisions that they prevent are T-bone type collisions at intersections and there is really no history of that at the 9 intersections. TAMC’s own Collision Data Map (link shown below) shows no fatalities or severe injury collisions in any of the 9 intersections between 2013 and 2018.
Collision Data Map – Transportation Agency for Monterey County (tamcmonterey.org)
Most (about 70 %) collisions on that stretch of 68 are due to rear end impacts which could actually increase since the roundabouts will cause all vehicles to slow down to 15-20 mph, 9 times on a 24/7 basis and potentially stopping to yield to side traffic, thus creating more chances for rear end collisions. Currently, vehicles on average may stop at only 2-3 of the 9 signals during non-peak commutes and even then, the signals can be seen from a distance, so drivers have adequate warning.
In spite of what is being promoted by Caltrans, that 8-mile stretch of 68 has a good traffic safety record according to data obtained directly from Caltrans by a public records request. (shown below) The collision rate has been below the state average since 2017 and the TAMC collision map show where and the type of crash on this stretch of highway. Unfamiliarity with the roundabouts historically cause more collisions, especially with numerous out of town people using that highway annually.
Hello
As an expat Brit where roundabouts of all sizes are standard, I have watched this discussion for some time but feel prompted to add my 2 pennies now. I drove many miles in the UK before we immigrated to the USA and generally loved roundabouts. Over the years I had reason to travel back and drive in the UK for family reasons and for work activities. I noticed over the years that roundabouts on most of the busiest roads now have part time traffic signals installed to regulate traffic in busy traffic hours. These traffic signals are necessary because the primary route through the roundabout will dominate and there are no gaps for traffic on side roads to enter if the rule of yielding to traffic already on the roundabout is obeyed.
I believe that if the costs of installing a synchronized traffic signal solution is indeed less than $1million then this should be trailed before a major investment for roundabouts is made. If a roundabout solution is installed, then the planner should include provision for rush hour traffic signals.