Less Traffic with Smart Stop Lights Act of 2019 This bill directs the Department of Transportation (DOT) to establish a Smart Technology Traffic Signals Grant Program. DOT may provide competitive grants to states, local, or tribal government entities for projects that improve the functioning of traffic signals to (1) reduce traffic congestion, (2) improve the safety and effectiveness of roadways, (3) reduce fuel costs for drivers, and (4) reduce air pollution. Grants may not be used to purchase, operate, or maintain an automated traffic enforcement system. The federal share of project costs may not exceed 80%, but DOT may waive such limit if an assisted entity can show extreme financial hardship.