North Yorkshire County Council will begin work on 22 May on a £1m scheme to strengthen Cawood Bridge and increase the bridge's capacity from 7.5 tonnes to 10 tonnes.
The project involves painting the swing bridge and installing steel plates to strengthen it. It is expected to take 17 weeks, with completion scheduled for 15 September.
The County Council originally intended to start the work earlier in the year, but after listening to the views of nearby residents it agreed a later start date, with the road closed only during the summer school holidays.
Barrie Mason, Assistant Director for Highways and Transportation, said: "This investment in strengthening the bridge will have long-term benefits for the local and wider community. It will ensure the bridge's longevity and help to retain local bus services.
"In timing these works, we have listened to the views of residents who use this bridge and we will continue to make every effort to minimise disruption and to ensure there is no conflict with maintenance on the diversion routes."
The bridge will close from 24 July to 2 September for installation of the steel plates and erection of scaffolding for use in painting the bridge. At other times, traffic lights will be in place to manage traffic. These will be monitored throughout the works to minimise the impact on road users.
Major strengthening of the bridge took place in 1986 and a weight limit of 7.5 tonnes was placed on it with an exemption for public service vehicles weighing less than nine tonnes. This arrangement continued until it was established that Department for Transport guidance stated structural limits applied to all types of vehicle and an exemption could not be made for buses.
Since autumn 2015, the commercial operator has used smaller buses to comply with the 7.5-tonne weight limit. Increasing the weight limit to 10 tonnes will allow larger buses to use the bridge, though not full-size ones. For all buses to use the bridge, the weight limit would need to be increased beyond 10 tonnes at a cost of about £8.6m.
Throughout the work, a slide show providing regular progress reports will be screened on a TV in the post office.
Next year, the County Council intends to replace the bridge's motor and operating system with new, custom-made equipment. This will require a closure of only a few days.
Update: 21 July
To enable the works to strengthen #Cawood swing bridge, as planned the road will be closed on Monday 24 July for six weeks. There will be no access across the bridge for vehicles, cyclist or pedestrians during this period.
In the first couple of weeks the contractor will be stripping the deck of the surfacing material and painting the inside of the parapets and lifting out and replacing a section of the steel road. It may appear possible to walk over the bridge at this time, it will not be safe to do so and the bridge will be closed to pedestrians.
During the closure the bridge will be swung open to river and will remain in that position until the strengthening works have been done to the nose end of the swing span.