>Al, you are 100 percent correct. The Bridge Railway could never have handled the daily passenger loads that BART does at the speeds BART runs in the tube. The Bridge Railway is great nostalgia as is the Key System; no doubt about it. Nice memories of a slow, enjoyable ride.

Ultimately, the limiting factor for the maximum speed on the Bridge Ry after the SP and SN went away was the stopping capabilities of the Key Units on the downhill part of the cantilever section, which was something on the order of 2+%.

In the early 1950s the Key and Toll Bridge authority ran some tests to figure out if the max speed could be raised above 35. These consisted of disabling the brakes in one car of a unit (which includes one axle of the center truck) and measuring the stopping distance down this grade for an emergency brake application.

It was discovered that the test unit would have struck the rear end of train stopped ahead even when big holed immediately upon the receipt of a red 11, which was the most restrictive indication given by the train control (i.e. when entering an occupied block). Actually it overran the theoretical rear end of this theoretical stopped train by 10 or 20 feet. In other words, in the worst case scenario, the stopping distance was too short to be safe.

It was then determined that reconfiguring the track circuits for longer blocks and modifying the cab signal apparatus on the units in order be able to go faster than 35 mph would have been prohibitively expensive given the declining passenger loadings of the day.

It's still amazing that the Bridge Railway was designed to handle 90 second headways with 10 trains in each direction at any given time, serving three different RRs. The power switch at Rincon Hill which sorted WB SP to the right and WB Key/SN to the left for entry into the East Bay Terminal was thrown by the train describer, which followed each train across the bridge. All this was accomplished in 1939, without computers nor solid state electronics of any kind (except for two vacuum tubes in the amplifier section of the code receiving apparatus on each Key Unit and cab signal-equipped SN car).

They Key used sanders, BARTD has never had them, which is a bit worrisome when the rails are wet.