Network Rail said trains between Edinburgh and Haymarket may be delayed by up to 15 minutes.
Disruption is expected until 10am.
Posting on Twitter, ScotRail wrote: ‘We've received reports of a vehicle striking a bridge between Edinburgh Park and Haymarket.
‘Services can continue to pass over the bridge at a reduced speed.
'Please keep an eye on our app and JourneyCheck as services may experience delays/cancellations’.