The 94-year-old Manthey Road over the San Joaquin River at the Mossdale Crossing will no longer be replaced per se.

Due to the distance from the nearby Interstate 5 bridges across the river, Caltrans had determined the current bridge — if it were replaced — would leave inadequate separation between bridges.

Instead the plan is to pool resources with Cambay Group — developers of River Islands at Lathrop to make the envisioned Golden Valley Parkway work as well as replacement for the Manthey crossing.

The Golden Valley Parkway — that intersects with River Islands Parkway by the Lathrop Target shopping center — will cross the river between the railroad trestle as well as the Bradshaw Crossing that carries River Islands Parkway into River Islands.

The existing bridge is too narrow plus lacks shoulders. It is unlikely that the bridge will be removed and instead may be used as a bicycle crossing or limited vehicle access.  Over a decade ago a structure was built next to it that holds the water  line that ferries treated surface water from the South San Joaquin Irrigation District to River Islands and Tracy.

By using Golden Valley Parkway to essentially replace the Manthey river crossing, Lathrop will have to determine whether Manthey north of the river should curve to the east to intersect into the Golden Valley Parkway.

The issue with Manthey Road on the south side of the river is more problematic.

Caltrans, with their original sign-off on the River Islands planned community, required Cambay Group to eliminate access to River Islands from Interstate 5 via the Manthey Road exit. That would mean Stewart Road would have to be blocked off at the railroad tracks.

River Islands Project Manager Susan Dell’Osso noted they have been working with Caltrans to determine if improvements can be made to the ramps at Manthey — longer acceleration and de-acceleration ramp lanes and/or auxiliary lanes are possibilities — that would allow access to River Islands via the Manthey Road exit on Interstate 5 to continue.

If the Manthey to Stewart Road access from Interstate 5 is retained, that will create five ways to ultimately access the 11,000-home planned community. River Islands Parkway and Golden Valley Parkway would cross the river

 Golden Valley Parkway would swing through the planned employment center where a Valley Link station for commuter rail service connecting to the BART station in Pleasanton-Dublin is planned. Golden Valley Parkway would connect to a future interchange on Interstate 205 where Paradise Road currently crossing beneath the freeway.

The fifth access to the planned community would be extending River Islands Parkway to connect with MacArthur Boulevard in Tracy where residents can also reach I-205.

Although there is no timetable for the Golden Valley Parkway bridge to be built, it is likely to occur within the next 5 to 10 years right around the time the 593-foot long Manthey Road bridge reaches the century mark.

Bridges over the San Joaquin River have a long and storied history in Lathrop. While the golden spike for the transcontinental railroad was actually hammered into the ground by Leland Stanford in Utah in May of 1869, the bridge at Mossdale Crossing wasn’t completed until September. That made it the last segment to connect the West Coast of the United States with the existing Eastern rail network that terminated at Council Bluffs, Iowa.

That bridge has since been replaced. It is still in operation today as a working train crossing.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com