The Colorado Senate has approved a bill requiring winter drivers to have snow-appropriate tires during winter months on the state’s mountain highways. The bill would require all motorists without four-wheel drive to use tires rated for snow conditions or carry chains or cables during snowy months. The requirement already applies to commercial vehicles. The bill originally set the requirement for Interstate 70, Colorado’s major east-west highway. Senators amended the bill to apply to other mountain highways, too, potentially endangering the bill’s prospects. One more vote is required in the Senate. The measure would then return to the House, which approved the bill earlier but in a different form.