iStock illustration

Nearly 6 in 10 likely voters support a proposed constitutional amendment to impose a higher tax rate on income above $1 million, a new poll shows.

A MassINC Polling Group survey of 987 likely voters published Thursday found 59 percent of voters said they would back imposing a 4 percent surtax on high earners, compared to 31 percent who would vote to keep the existing flat personal income tax rate and another 10 percent of voters who do not know or refused to say where they stand.

That represents a sizable lead for the measure with fewer than three weeks to go until the proposal reaches its key vote following a years-long, stop-start journey.

If the question prevails on Nov. 8, Massachusetts would continue to tax all personal income up to $1 million at the current rate of 5 percent and newly subject earnings above that threshold to an effective tax rate of 9 percent.

Analysts project the higher rate will generate $1.3 billion in annual revenue for the state, which the question seeks to direct toward transportation and education investments.

MassINC conducted the new poll, sponsored by The Barr Foundation, between Oct. 5 and Oct. 14. The organization’s senior research director Richard Parr said its margin of error was 3.2 percentage points.

Asked to rate the condition of Massachusetts transportation, 52 percent responded “fair” and 26 percent responded “poor,” while 18 percent said the system is in “good” condition and only 3 percent dubbed it “excellent.”

How policymakers should fix those concerns is about as divided as can be: 47 percent of likely voters answered that Massachusetts needs only “to fix and maintain our current transportation system,” while another 47 percent said “we need major changes to the way we get around in Massachusetts.”

And despite the frustration apparent with the state’s transportation system, most voters still favor Baker’s approach to the issue as the top elected official: 64 percent strongly or somewhat approve his management of transportation issues, compared to 31 percent who strongly or somewhat disapprove.

“Voters are not happy with the state of transportation in Massachusetts, but they’re not taking it out on Charlie Baker,” Parr said. “It will be interesting to see if the next governor inherits Baker’s suit of armor on this issue.”

The MBTA has drawn much of the attention in recent months amid a federal investigation that flagged persistent safety issues and a month-long shutdown of the Orange Line, which a sizable majority of voters felt was worth the inconvenience, according to the MassINC poll.

In fact, 59 percent of respondents said they believe the T should focus on making repairs as quickly as possible, even if that entails shutting down entire subway lines. Thirty-two percent said the MBTA should keep subway lines open as much as possible, even if that extends the duration of repairs.

Support was slimmer, but still a majority, among those who bore the brunt of the Orange Line closure. Among voters who said they were personally impacted by the shutdown, net support for faster repairs over keeping lines open was 10 percentage points; among voters not personally affected by the Orange Line diversion, net support for speedier maintenance was 34 percentage points.