MONTPELIER (AP) -- The state of Vermont has been working for years to improve cellphone coverage and now testing is underway to determine how successful those efforts have been.

Mike Ray and Jo Wilson of the Colorado company Pericle Communications spend their days driving the roads of Vermont with five cellphones mounted in coolers on the roof of their vehicle.

The company was hired by the state with help from a federal grant to measure cellphone signal strength in different parts of Vermont.

Ray tells Vermont Public Radio that computer modeling could estimate cell strength in different locations, but the only way to know for sure is to try it.

The state’s goal is to ensure the major carriers are providing service to all of Vermont’s interstates and well-traveled state highways.