The Tribune

By NEIL HARTNELL

Tribune Business Editor

nhartnell@tribunemedia.net

THE GOVERNMENT’S advisers have ruled out replacing Eleuthera’s Glass Window Bridge with a four-lane highway because the island’s projected growth will not generate sufficient traffic volumes to warrant such expansion.

The results of a traffic impact study, released ahead of a public consultation on the bridge’s proposed replacement, said the two-lane solution - with traffic flowing both ways - offered sufficient capacity for commercial and passenger vehicles for the next 20 years and beyond.

Even with a so-called “high growth” scenario, which would see a 5 percent annual increase in traffic, the Government’s engineers and planners said the 2,200 daily vehicles this would generate by 2042 - a doubling of today’s 1,100 autos passing over the Glass Window in both directions - was still far below levels requiring a four-lane solution.

“A high-level planning analysis of the capacity of the Glass Window Bridge was undertaken to assess the potential need for a four-lane structure based on 20-year travel demand forecasts. The requirement for widening is based on the volume-to-capacity ratio of the forecast 20-year traffic volumes to published theoretical lane capacities,” the report said.

“The level-of-service transportation capacity of a two-lane bridge was estimated between 11,500 to 14,000 average daily vehicles, or 700-to- 800 vehicles an hour in the peak direction. In the 2042 horizon year, the volume-to-capacity ratio was found to be less than 0.26 in all time periods, directions and traffic volume growth scenarios considered within the assessment.

“Therefore, the two-lane Glass Window Bridge offers a significant amount of spare capacity and does not require widening to a four-lane cross-section based on projected daily and hourly travel demands. In the case where Eleuthera experiences significant urbanisation, investment in its tourism industry and a rising population, the bridge would still have significant capacity to accommodate an increase well beyond 20,000 persons on the island.”

A May 2022 study found that daily traffic passing across the Glass Window Bridge ranged between 840 to 1,130 vehicles per day, with greater daily traffic on weekdays. Heavy vehicle trucks accounted for between 12 percent to 21 percent of all daily traffic. Bus traffic represented about 2 percent of all traffic on Thursday, Friday and Sunday.

Outlining the rationale for replacing the critical transport link between north and central/ south Eleuthera, the report added the Glass Window Bridge faces an “extremely aggressive environment” in rough weather and high seas when water crests the roadway and it becomes challenging to cross. The existing infrastructure has been repeatedly acknowledged by the Government as having deteriorated, and been in poor condition, for many years.

“Options considered as part of the concept design study included bridge replacement along various alignments to the west of the bridge, and with profiles that are relatively higher than the existing bridge which is at an elevation approximately 40 feet above sea level,” the Government’s planners said.

“The option of having a new bridge built on the existing alignment was discarded as it would significantly impact traffic during construction given the condition of the existing bridge, and given its current performance with severe overtopping and wave impacts several times each year. The option of rehabilitating the existing bridge was also discarded at this stage as the severe overtopping and wave impacts would not be addressed, nor would the potential bedrock issues along the site.

“Additionally, the existing bridge is in poor condition with severe deterioration of the girders and the intermediate supporting underneath the girders. Further to that, the girders were not originally designed to accommodate an intermediate support. The various options considered did not take the utilities into account as the option of attaching the utilities to the structure is similar for all options considered.”

The preferred solution is “the construction of a pre-cast pre-stressed side-by-side box girder/slabs bridge on an alignment approximately 60 feet west of the existing structure”. The Government’s planners added: “The 20-span bridge would have an overall length of 1,260 feet with eight 120 foot main spans and six 50 feet approach spans.

“Three hundred and thirty-five foot long retaining walls would be required on the approaches on the Bight side. The elevation of the new bridge riding surface at the channel location would be approximately 13 feet higher than the existing bridge at approximately 53 feet above sea level. The abutments and piers for this structure would be founded on drilled shafts on land.”

Describing this as the superior solution, the Government’s planning, engineering and design consultants said it “greatly reduces, if not mitigates, the effects of the wave action from the Atlantic Ocean, while also being comprised of solely out-of-water piers. This option is less intrusive on the ecological environment and requires minimal in water works. Using an alignment adjacent to the existing structure will significantly reduce any impact to users during construction”.