Not much if DOT proceeds with their current plans which maintain many car lanes and conflicts with curbside uses between Dyer and 8th Avenues.
As part of the Better Buses Action Plan, DOT intends to improve bus speed by 25% by 2020. the M42 was an easy choice, at 4mph or 25% slower than other buses in Manhattan and a third of W 42nd street users traveling on bus (probably more if it was faster).
DOT presented to Manhattan Community Board 4 a plan to install dedicated bus lanes for the M42. across Manhattan. The plan seems to be well thought out between Dyer and 12th Avenues , but between Dyer and 8th Avenue, the plan falls apart. There are no proposed eastbound bus lanes between Dyer and 9th Avenue , with two lanes dedicated to the tunnel traffic. On the block between 9th and 8th the bus lanes are along the curb, when we know that multiple buses and jitneys block the lanes the whole day.
These layover would slow down buses for the whole route . This block is very complex but we expect DOT to come back with a better mousetrap.
See the full presentation here