ROCHESTER — As the Mayo Clinic seeks state money to help with its expansion plans, Minnesota’s third-largest city is feeling the strain from the rapid growth it has already seen.

Rochester’s population has doubled since 1970 to more than 107,000, and is projected to grow by another 32,000 in 20 years. Since 2000, the city has annexed nearly 10,000 acres, and farm fields have given way to housing developments and strip malls, especially on the northwest side.

But city planner Phil Wheeler tells Minnesota Public Radio a lot of that development hasn’t been paying for the infrastructure needed to support it.

Rochester expects to need $2.4 billion for transportation infrastructure in the next 25 years. Officials expect revenue for it to reach only $1.6 billion, leaving a gap of about $816 million.