Tests are being carried out to check whether the track of the £116m Cambridge to St Ives guided busway could move in hot weather.
Contractors BAM Nuttall is testing soil from under the tracks to check if some of the foundations used are suitable, Cambridgeshire County Council said.
It had raised concern that BAM Nuttall may not hit its mid-June deadline for submitting the results.
The tests are among six issues holding back the completion of the busway.
Work on the site began in 2007 and it was planned to open in spring 2009.
BAM Nuttall set a self-imposed timetable at the end of April so residents can track the progress they are making.
Revised designs have also been submitted to address the issue of water sitting on the surface of a park and ride site.
Bob Menzies, the council's head of busway delivery, said: "As we have said for some time, until the (soil) calculations are completed we will not know if any work will be needed.
"But it would be wrong to accept the busway without knowing the results."
The guided busway will involve vehicles using a special roadway or track solely for their use.