The state Department of Transportation has developed a list of alternatives for maintaining a safe, reliable travel route across the Penobscot River between Prospect and Verona. They are:

. Adding supplementary cables on each side of the bridge for short-term repair costing about $9 million.

. Replacing the main cables, which is difficult and costly to do while the bridge is open. Cost: $35.9 million.

. Constructing a new segmental concrete bridge for $25.7 million.

. Constructing a new cable-stayed bridge for $30.2 million.

. Constructing a new steel arch bridge for $36.3 million.

. Constructing a new suspension bridge for $38.8 million.

All of the estimates are for construction costs only and do not include any engineering expense. The estimates also do not include the cost of removing the 71-year-old bridge, if that were necessary.

The most feasible option will be determined through a process under the National Environmental Policy Act, which is designed to balance competing demands and examine how each option would affect the community, the natural environment and human health and welfare.

The Federal Highway Administration, which likely would provide 80 percent of the construction costs for whatever alternative is chosen, will review all alternatives and determine the preferred alternative.

That process is estimated to take at least 18 months, although it could take much longer. DOT officials already have begun the preliminary steps, although no date has been set for a scoping meeting, the first chance that local residents would have to voice their opinions.

The department also has set in motion the funding process for any project by placing the bridge on its priority projects list, which has been forwarded to the state’s congressional delegation.