The Traffic Study develops a 20-year traffic forecast (design year of 2042) based on existing traffic counts and historical growth patterns to assess the impact future growth may have on this bridge facility.

​

Existing traffic counts were undertaken between 6:00 AM Thursday, May 12th and 6:00 AM Monday, May 16th 2022 through a combination of manual and video methods which recorded northbound and southbound traffic along the Glass Window Bridge.

​

The traffic data gathered indicates the following:

​

• Daily traffic was found to range between 840-to-1,130 vehicles/day, with greater daily traffic on weekdays;

• Throughout a full day of travel the magnitude of northbound and southbound traffic was fairly similar, with the northbound typically maintaining more than 50% of the daily traffic;

• The heavy vehicle truck component of vehicle was found to be significant, ranging from 12%-to-21% of all daily traffic. Bus traffic represented approximately 2% of all traffic on Thursday, Friday and Sunday;

• A review of the ‘trip purpose’ information found that local drivers represented about 60% of all trips, with the proportion increasing on Sunday May 15th;

• Typically, the afternoon peak hour was found to be greater than the morning peak hour while coinciding as the daily peak hour; and

• On Thursday-to-Saturday, northbound traffic was found to peak during the morning period (Approx. 9:00 AM) while southbound traffic would peak during the afternoon period (Approx. 5:00 PM).

​

A conservative traffic growth rate was established based on a review of The Commonwealth of the Bahamas, Population Projections 2010 – 2040 Report. The population projects were projected as low (0.77% growth/year), medium (0.96% growth/year) and high (1.2% growth/year) variant scenarios to estimate population growth over

the 30-year period. The population projections were based on an analysis of past trends in births, deaths and migration.

​

A range of growth scenarios have been considered:

​

• In the case of low growth scenario which reflects the changes in traffic between 2005-and-2022, effectively no additional traffic would be expected to occur beyond the 2022 average daily traffic recorded as part of this study.

• Regarding a more conservative low-to-medium growth rate, a 1% traffic growth which corresponds to the Medium Variant population growth scenario for the Bahamas that represents the ‘most likely scenario’.

• Finally, an advanced growth scenario which would exceed previous growth estimates by adopting a 5% annual traffic growth rate. This growth projection reflects an abnormal amount of growth over an extend period of time for regarding population increases and development investment within the tourism industry on the island of Eleuthera, and that local travel patterns continue to rely on the Glass Window Bridge.

 

A low-to-medium growth scenario assuming the 1% annual increase in traffic and the May 2022 traffic count, the following 20-year (2042) traffic volumes are projected along the Glass Window Bridge:

​

• 1,320 vehicles/day in both directions, which represents an increase of approximately 220 vehicles/day above the traffic observed in May 2022;

• Of the 1,320 vehicles/day, approximately 26 buses and 190 trucks would utilize the bridge on a daily basis; and

• The highest peak hour of up to 160 two-way vehicles, or 110 vehicles in a single peak direction, which typically occurs in the afternoon peak period.

​

A high growth scenario represented by a 5% annual increase in traffic and the May 2022 traffic count, the following 20-year (2042) traffic volumes are projected along the Glass Window Bridge:

​

• 2,200 vehicles/day in both directions, which represents an increase of approximately 1,100 vehicles/day above the traffic observed in May 2022;

• Of the 2,200 vehicles/day, approximately 44 buses and 350 trucks would utilize the bridge on a daily basis; and

• The highest peak hour of up to 265 two-way vehicles, or 185 vehicles in a single peak direction, which typically occurs in the afternoon peak period.

​

A high-level planning analysis of the capacity of the Glass Window Bridge was undertaken to assess the potential need for a 4-lane structure based on 20-year travel demand forecasts. The requirement for widening is based on the volume-to-capacity ratio (v/c ratio) of the forecast 20-year traffic volumes to published theoretical lane capacities. The v/c ratio can also be expressed as a level-of-service of the roadway. It is desirable to maintain a minimum level-of-service “C” or “D” threshold (measured A-to-F, where LOS F represents significant roadway congestion) on any particular roadway facility.

​

The level-of-service “D” transportation capacity of a two-lane bridge was estimated between 11,500-to-14,000 average daily vehicles, or 700-to-800 vehicles/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 4-lane cross-section based on projected daily and hourly travel demands. In the case where Eleuthera experiences significant urbanization, 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. Refer to Appendix D for the complete analysis including existing traffic volumes, traffic growth projections based upon low-to medium and high-growth population projections, and the capacity for both a two lane and four lane bridge facility.