Under Nashville Mayor Megan Barry's $5.2 billion transit plan, commuters heading away from downtown on a proposed Charlotte Avenue light rail line would get no farther than Interstate 440 near 31st Avenue North.

That's where the route is set to end, stopping short of three hot West Nashville neighborhoods — Sylvan Heights, Sylvan Park and The Nations — that on paper seem like the type of places where residents would welcome new transit.

► More:Mayor Barry unveils sweeping $5.2 billion transit proposal for Nashville with light rail, massive tunnel

► More:The lurking question on Nashville's transit plan: What about self-driving cars?

The length of the 2.5-mile Charlotte Avenue route has drawn scrutiny from two West Nashville council members, Kathleen Murphy and Mary Carolyn Roberts, who say the plan misses out on areas that want and need the service.

Roberts said it would be difficult for her to support the transit plan if it isn't altered to extend farther down the Charlotte Avenue route.

Murphy, who represents Sylvan Park and Sylvan Heights, said she wants to hear the administration's explanation, but believes the Charlotte Avenue route should go to at least White Bridge Road. She said city is also losing out on potential riders from Robertson and Montgomery counties who enter Nashville from Briley Parkway.

"I've heard concerns from my constituents," Murphy said. "It's missing some pretty dense neighborhoods, being Sylvan Park and The Nations. That's definitely something I have voiced to the administration."

When asked whether she would back the plan in its current form, Murphy said she supports giving Nashville voters the ability to vote on transit, but wants to hear more community feedback before deciding where she'll come down on all details of the plan.

"That's the million-dollar question," Murphy said of her position on the plan, then rephrasing: "Well, I guess it's more than a $1 million question."

Mayor's office points to cost to explain route length

Cost is the primary reason the Charlotte Avenue light rail line isn't longer, Barry spokesman Sean Braisted indicated in a statement.

"As Mayor Barry said at the announcement, this should not be seen as a finish line, but as a starting point for a regional public transportation system," Braisted said.

"We absolutely want these lines to go further, but we also wanted to be fiscally responsible in our cost estimates to ensure that there are no issues with overpromising and under-delivering in a first phase of construction."

► More:Nashville sales tax rate would tie Chicago for nation's highest under Mayor Barry transit plan

Braisted said the mayor's transit plan will be "flexible enough" so that transit lines can be extended closer to the county line as additional federal, state or local funds become available.

Charlotte Avenue shortest, least expensive of 4 light rail corridors

At 2.5 miles, the Charlotte Avenue light rail line is among the shortest in the transit plan. The Murfreesboro Pike light rail line would extend 8 miles from downtown; Gallatin Pike, 6.4 miles; and Nolesnville Pike, 5.8 miles. A Northwest light rail line that would extend north from Charlotte Avenue would be 2.2 miles and run along existing rail lines.

A new underground downtown tunnel, where each of the light rail lines would connect, would be 1.8 miles long.

► More:Downtown Nashville underground tunnel to be part of Mayor Megan Barry's transit plan

Neither the Northwest line nor a separate light rail connection between Murfreesboro Road and the Nashville International Airport — also part of Barry's plan — were included in the region's nMotion transit plan adopted by the Metro Transit Authority last year. In contrast, nMotion called for light rail on Charlotte to expand far past White Bridge Road.

The Charlotte Avenue route also comes with the smallest price tag. Its projected cost is $457 million, compared to $789 million for Gallatin Pike, $666 million for Nolesnville Pike and $663 million for Murfreesboro Pike. The downtown tunnel is projected to cost $936 million. The light rail airport connection is projected to cost $165 million, with funding coming from airport revenue.

Roberts, whose district includes The Nations, said the Charlotte Avenue light rail line should extend even farther west than White Bridge Road so light rail could reach the Nashville West Shopping Center.

"It's going to be hard for me to get behind a plan that doesn't include my district," Roberts said, adding she had assumed that light rail extended past 46th Avenue North because of early renderings released this summer on Barry's light rail plan. "Then when I saw that it didn't, I have reservations."

"The density in Sylvan Park and The Nations, and upcoming Charlotte Park — those are I would think your ideal riders."

Mayor's office: Each new mile to route would cost $100 million to $125 million

Barry has outlined increases to four taxes, including the sales tax, that she wants voters to approve via referendum on May 1 to pay for the transit project. To get her plan on the ballot, the Metro Council would need to approve the referendum's language in January.

Former Mayor Karl Dean's controversial bus rapid transit project called The Amp, which died during his final year in office, faced pushback in affluent neighborhoods along West End Avenue, where the line would have traveled.

But those neighborhoods are a couple of miles from Sylvan Park and The Nations and considerably wealthier.

► More:The lurking question on Nashville's transit plan: What about self-driving cars?

Braisted said each mile added to the Charlotte line would cost an additional $100 million to $125 million, meaning it would cost an additional $400 million to $500 million for the Charlotte Avenue route to go to Nashville West Shopping Center.

He said doing so could not be made without sacrificing service along another corridor or further increasing taxes to a rate that the mayor's office has determined unreasonable.

Braisted said the administration plans to have cost estimates and assumptions reviewed and vetted by an independent CPA firm for accuracy.

"We will continue receiving and reviewing feedback from elected officials and members of the public to ensure the plan we present to the voters in May will be broadly supported throughout the community," he said.

To hear public input, the mayor's office has organized six community meetings along each of the light rail routes. The Charlotte Avenue-focused meeting is set for 6 p.m. on Nov. 9 at the Lentz Public Health Center.

Light rail lines by cost

Downtown connection tunnel — $936 million

Gallatin Road — $789 million

Nolensville Road — $666 million

Murfreesboro Road — $663 million

Charlotte Avenue — $457 million

Northwest Corridor — $260 million

Murfreesboro (Airport) – Light Rail Transit — $165 million

Light rail lines by length (miles)

Gallatin — 6.4

Murfreesboro — 8

Nolensville — 5.8

Charlotte — 2.5

Northwest — 2.2

Downtown Tunnel — 1.8

Reach Joey Garrison at 615-259-8236, jgarrison@tennessean.com and on Twitter @joeygarrison.