Repairs to the bridge over the Noordhollandsch Kanaal at Purmerend on the A7 motorway may increase journey times for motorists by an hour or more for the next five months, the transport ministry’s roads department has said.

The work will take place between April 5 and September 1 and during that time only one half of the bridge will be accessible. Narrower lanes and speed restrictions will also be in place.

As of Thursday sliproads 4 and 5 in the directions of Hoorn and Zaandam have been closed off so work can start on one side half of the bridge. Travel times for motorists travelling between Hoorn and Amsterdam could be as much as an hour longer. Once that side has completed, it will be reopened and work will start on the other.

The bridge, which dates from 1976, needs strengthening to support heavy traffic. The work includes replacing concrete supports with tonnes of reinforced steel.

The repairs were originally calculated to take eight months but that was cut to five after pressure from local businesses and the Dijklander hospital in Purmerend and Hoorn. Doctors at the hospital are still worried emergency help will be hindered by the work as the A7 is one of the two main routes into Noord Holland.

The hospital has opted for consultations by phone and medical specialists can stay the night at the hospital if needed so they won’t get stuck in traffic.

The transport ministry has advised commuters to work from home, use public transport, or share a car. If 20% of people do this, the delay could be brought back to half an hour, officials said.