A contractor is getting ready to replace a bridge through I-295 in Portland, but there shouldn’t be a prolonged closure of the key traffic artery.

The Maine Department of Transportation says the start of the nearly $21 million project involves a reconfiguration of the roadways beneath the bridge to improve mobility and safety.

Cianbro, the contractors, will build the replacement bridge alongside the existing bridge, then slide it into place.

Officials say the highway will be closed for fewer than three days.