PIERRE, S.D.(WNAX)- The South Dakota Department of Transportation will be posting signs on twenty-one bridges on and near interstates due to a federal requirement on emergency vehicle weight limits.

David Coley, a D.O.T. bridge management engineer, says the rules allow some of those vehicles to exceed current limits at times.

Coley says large emergency vehicles can cause some issues.

Coley says the department has worked with fire departments and other first responders in finding alternative routes where possible.

Those signs should be in place by the end of the month.