The highway’s outdated design — including the narrow lanes and no shoulders in places — can make it a scary drive. City officials say the design has contributed to a high crash rate.

The department took the unusual step recently of unveiling two options. A precedent for this was set by the Metropolitan Transportation Authority, which operates the subways, when it offered two options for addressing the closing of part of the L line for Hurricane Sandy-related repairs.

What is being proposed?

Plan A: Build A Temporary Highway

A temporary elevated roadway would be built at the level of the promenade, with part of the promenade converted into vehicle lanes. This would allow the city to replace the entire triple cantilever, while six lanes of traffic that currently run through its bottom two levels are diverted to the top.

City officials have said they prefer this option because they could do the most work in the shortest time. They would widen lanes and add shoulders to provide access for emergency vehicles, and also look at ways to improve nearby parks and pedestrian and bike connections.

With a temporary highway in place, drivers would see fewer delays. There would be less traffic being rerouted onto local roads.

Construction Time: 6 years

Cost: $3.2-$3.6 billion

Plan B: Incremental Lane Closures

The B.Q.E.’s six lanes would be closed one by one to reroute traffic around ongoing construction in what city officials call the traditional approach. Work would have to be stretched out over a longer period of time, and the schedule and cost are less certain.