MassDOT said today it will experiment next week with letting Silver Line buses use a ramp from the South Boston Haul Road to I-90 that, if nothing bad happens, could lead to shorter rush-hour rides between downtown and Logan Airport and Chelsea on Silver Line bus routes.

Bus drivers will gingerly test out the ramp on Aug. 27, 28 and 29, MassDOT sasys.

Transit activists have been advocating for Silver Line use of the ramp for years, arguing that letting the buses bypass some South Boston traffic could lead to better rides.

Since the opening of the Ted Williams Tunnel and associated turnpike lanes, the ramp has been limited to State Police and other emergency vehicles.

State officials have long balked at letting the longer Silver Line buses onto the ramp for safety reasons - and safety is the main thing that will be at issue during the tests, the state says:

To safely merge onto I-90 eastbound, Silver Line bus operators will only use the ramp when speeds are at 30 mph or less. In addition, prior to entering the ramp, drivers will be notified that the ramp may be used for travel by a lane use signal and then by an MBTA Inspector on the roadway. A radar detector installed at the access ramp merge point near the I-90 eastbound tunnel portal will be collecting the speeds of motor vehicles on I-90 eastbound to help determine whether the Silver Line buses can safely merge. This radar detector will automatically communicate to a signal on the Massport Haul Road. The VMS board will be manually turned on and off at the beginning and end of the afternoon peak travel period.

MassDOT adds: