Rail proponents and opponents don't agree on much when it comes to assessing the costs and benefits of Honolulu's planned elevated commuter train.

In fact, about the only thing they agree on is that the other side is misleading the public about key facets of the public transit project.

That leaves residents the task of sorting through numerous, often conflicting claims about the impacts of rail ahead of a key Nov. 4 vote that will dictate the project's future.

The basis for much of the city's evidence supporting rail comes from the November 2006 Alternatives Analysis, which was prepared by transportation engineering firm Parsons Brinckerhoff. The report determined that a train reduced traffic congestion and increased public transit ridership more than managed highway lanes. A new elevated highway also would cost more to build and operate in the long term, according to the $10 million study.

Stop Rail Now, which has not done a comparable study, contends the city did not conduct a rigorous, good-faith analysis of the managed-lane option. Stop Rail Now contends its analysis shows that a new elevated freeway and bus rapid transit system from Waiawa to Iwilei would cost less to build and operate than a train.

There are numerous points of contention between city officials and Stop Rail Now. Their disputes surround a range of rail-related issues including costs, traffic impacts, energy efficiency, federal funding, noise and ridership.

Here's an assessment of those issues:

ISSUE: TRAFFIC CONGESTION

What the city says: Rail will reduce future traffic congestion.

What Stop Rail Now says: Traffic will be far worse in the future with rail.

The facts: Both statements are factual. That's because the project, which would link East Kapolei to Ala Moana, will help take more autos off the road, but will not prevent traffic from worsening in the future. According to the Alternatives Analysis, the initial 20-mile rail system will reduce peak-period vehicle hours of delay by 11 percent in 2030 compared with a so-called "no build" scenario.

The same study found that even with the transit system, there will be an estimated 57 percent increase in traffic on H-1 during the morning rush hour in 2030 compared with 2003. If the transit system were not built but a few improvements were made to the freeway and bus system, traffic would increase by 64 percent by 2030.

ISSUE: PROJECT COSTS

What the city says: The initial 20-mile segment will cost $3.7 billion — an amount that includes an added $1 billion for contingencies. The full alignment from West Kapolei to Waikiki is estimated at about $5 billion, according to the Alternatives Analysis. That includes a shortened $350 million spur from the Honolulu International Airport to Middle Street, which was necessitated by a main route that now runs through Salt Lake.

Those figures, which are in 2006 dollars, were based on recent large-scale O'ahu construction projects and U.S. Navy construction cost data for Hawai'i. They will be updated in an upcoming draft environmental impact statement.

What Stop Rail Now says: The full rail project will cost $6.4 billion. The group bases its figure on the estimated construction costs of Honolulu's failed 1992 rail project. Those costs were adjusted up for inflation and to provide a 33 percent allowance for contingencies.

The facts: No one knows for sure how much the rail system will cost. Recent events including a nationwide credit crunch and a slowing Hawai'i economy only add to the uncertainty.

If history is any indication, train projects tend to cost more than anticipated during their Alternatives Analysis phase. Recently built rail systems, on average, experienced 40 percent cost overruns, according to an April report by the Federal Transit Administration. The agency analyzed 21 federally subsidized train projects that began operations since 2000. Some of those increases were driven by changes in scope of the projects.

The city contends Honolulu's project won't go over budget because the FTA now requires cities to create more stringent cost estimates.

ISSUE: ENERGY EFFICIENCY

What the city says: Modern rail is energy efficient and environment friendly.

What Stop Rail Now says: Modern rail transit is less energy efficient than autos.

The facts: Whether rail is more energy efficient and reduces air pollution hinges on factors such as ridership and the fuel used to generate electricity.

A full train uses less energy per passenger mile than an auto with one occupant. On average, rail transit requires less energy per passenger mile than autos, according to the Department of Energy. However, because of differences in routes, train technology and other factors, the energy intensity of heavy rail systems varies substantially from city to city. In some cases rail systems are less energy efficient than the average auto, in part because trains run all day often with fewer passengers in off hours and in the opposite direction of rush-hour traffic.

ISSUE: PROPERTY TAXES

What the city says: The initial 20-mile rail system can be subsidized without any increase in property taxes. The city's current financial plan only accounts for construction of the initial 20-mile East Kapolei to Ala Moana segment. No funds have been set aside for spurs to Waikiki, the University of Hawai'i-Manoa, the airport and West Kapolei.

What Stop Rail Now says: The city will need to raise property taxes more than 40 percent to pay for the full 28-mile rail system. The group claims the total system will cost $7.5 billion in 2006 dollars including cost overruns.

The facts: Honolulu taxpayers are expected to bear about $3 billion of the project's costs via a half-percentage point excise tax surcharge that expires in 2022. They could be asked to pay more, if the project is over budget or if tax collections don't meet expectations. In that case the two major potential sources for tax revenues are the city's property tax and the state excise tax.

The city may ultimately need to rely on added tax revenues if the 20-mile segment is over budget, or if the city opts to proceed with the construction of spurs to Waikiki, the UH-Manoa, the airport and West Kapolei. However, just how much added money the city will need depends on the level of future transit tax collections and the amount of cost overruns, if any. That means it's impossible to gauge how much property taxes would need to be raised in such a circumstance.

ISSUE: GENERAL EXCISE TAXES

What the city says: The financial plan for rail is prudent and conforms with strict federal requirements.

What Stop Rail Now says: The financial plan relies on unrealistic excise tax estimates.

The facts: Whether transit tax collections are sufficient to pay for the train depends in large part on whether the state's current downturn lasts a year or two or becomes a prolonged 1990s-style economic slowdown.

Plunging visitor arrivals and slumping real estate and construction sectors are forcing the state to reduce tax collection forecasts. City officials acknowledge that near-term transit tax collections could be lower than predicted. However, the city hopes that any near-term revenue shortfall could be offset by an economic rebound in future years. Additionally, a slower economy could result in lower labor costs.

ISSUE: FEDERAL FUNDING

What the city says: Federal Transit Administration and Congressional officials have almost guaranteed city officials that they will receive $700 million to $948 million (in 2006 dollars) in federal funds to help pay for the project.

What Stop Rail Now says: The federal government won't provide that money to Honolulu.

The facts: Officially, FTA officials have said it's too early to tell whether Honolulu will get federal funds or to determine how much those funds might be. However, Honolulu is in a strong position to attract federal money because the city plans to pay the majority of the project's costs.

Still, Honolulu isn't expected to find out for sure how much federal funding it will get until 2011.

Meanwhile, the city plans to start construction on the East Kapolei to Waipahu segment in December 2009. The city has argued that a faster timetable will help reduce costs while allowing limited service to launch in late 2012. Critics contend the city's timetable is not realistic and could result in a major burden for local taxpayers, if federal funds don't come through as planned.

ISSUE: NOISE

What the city says: Modern rail is quiet.

What Stop Rail Now says: Steel-wheel-on-steel-rail trains are an environmental blight. A Vancouver, Canada, train, which is similar to the system planned for Honolulu, generates 79 decibels of noise at a distance of 50 feet, according to the group.

The facts: Just how noisy the train will seem depends on a variety of factors including who manufactures the trains and the level of existing ambient noise in a community and the frequency of noise. Modern trains generate 72 decibels to 80 decibels of noise at a distance of 50 feet, according to the city. Generally, 75 decibels equates to the noise made by a vacuum cleaner at five feet, or a jet flying 5,000 feet overhead.

That's less noisy than a city bus, which generates a maximum of 83 decibels at 50 feet of distance, according to the city. However, trains will operate at a higher frequency than the typical bus route. Trains will operate at a frequency of about 400 times a day from 4 a.m. to midnight.

ISSUE: RIDERSHIP

What the city says: A train, when combined with TheBus, will increase overall mass-transit ridership to 7.4 percent of total transit trips in 2030, up from 6.1 percent projected if the commuter rail line is not built. That's a 21 percent increase.

What Stop Rail Now says: Train ridership will not meet expectations because people will continue to prefer driving their autos to work.

The facts: High gasoline prices coupled with newer, faster train systems are helping boost the popularity of public transit. However, in Honolulu, public transit ridership gains overall have not kept pace with population increases.

In addition, ridership on new federally subsidized trains, on average, is lower than anticipated, according to an April report by the FTA. The study found that 19 recently opened federally subsidized train projects are expected to carry, on average, 74.5 percent of their originally forecast ridership.

Honolulu city officials contend the FTA now is requiring cities to create more stringent ridership estimates. That means Honolulu's project should meet or exceed ridership estimates, according to the city.