The TransNet sales tax extension for transportation projects faces a tough road to approval in November, but a signed statement last week from nine elected North County officials should go a long way toward persuading voters to support it.

This extension of the half-cent sales tax for county transportation projects is too important to fail.

Members of the Board of Supervisors, some North County legislators and others have said the San Diego Association of Governments' spending plan gives too little emphasis to highways. But in a Friday opinion article, eight North County mayors and one mayor pro tem wrote that they have heard the public's concerns and "pledge to work for more improvements to our local roads and highways … during the next regional update of the Regional Transportation Plan."

Those are reassuring words.

TransNet, if approved, would pay for just a small part of SANDAG's overarching transportation plan -- about $14 billion out of $42 billion in spending on freeways, surface streets and mass transit. The 2030 Mobility Plan identifies many more projects than SANDAG has chosen to fund. So the agency already has a list of vetted highway projects that deserve funding.

It's too late to change the TransNet proposal that will go to voters Nov. 2. But by law, the Mobility 2030 Plan must be reviewed every three years. That review process already has started. The nine city officials who have promised to seek more highway funding have said, in effect, "We hear your concerns and we will respond to them." Seven of those officials are SANDAG representatives; the other two are alternates.

But those nine representatives do not constitute a majority of the 19-member SANDAG board. (SANDAG can change the Mobility Plan by a simple majority vote of the board; the majority must represent a majority of county voters.)

We hope all 19 members of SANDAG give a clear sign that they understand that the revised 2030 Mobility Plan needs to give greater emphasis to highways. Highways are the primary way people move here. Even for mass transit to work, people need better highways.

TransNet has run into considerable opposition from elected officials and many others who feel -- correctly -- that the spending plan spends too little on highways. North County commuters stuck in daily traffic jams know that they are right.

TransNet needs approval from two-thirds of voters to pass. To get that, it will need the support of all our local elected officials.

SANDAG board members are honorable people. They already have begun work on revising the Mobility Plan, giving them the perfect opportunity to give greater priority to highway construction. Their good-faith assurances should be sufficient to bring around most of their critics.

If they choose to do this, they can save TransNet. If not, it is likely to fail. That would be a disaster for our community.