4.1.4Designing the Traffic Guidance Scheme#

The site is located on a high-speed multi-lane divided road and, to accommodate a work zone on one carriageway, the left-hand lane will be temporarily closed to traffic. The following notes and discussion are based on the Queensland MUTCD and QGTTM documents (July 2021), including the requirements and options specific to Queensland.

The layout and order of the TTM elements of this TGS design may be completed in different ways, and this is just an example of one way that the Designer in this scenario has adopted.

1. 1.As part of the TMP design, the required method of control was identified, and the general worksite layout required for the works to occur safely was determined. In this scenario, the outcome of the planning process was to implement a 'traffic past the worksite' approach using a static worksite with a single lane closure and using traffic control as required in the 'open' lane to accommodate the works.

1. 2.The contractor requires 50 m of physical working area and has requested an additional length of 50 m to allow for ingress / egress / parking. This results in a work area of 100 m. Due to the full lane being replaced, workers on foot will be within 1.2 m of traffic and the full length of the 100 m work area will be signed at 40 km/h.

1. 3.From the TMP, work area separation is via lateral separation ('PAST' the worksite) and delineation / separation using traffic cones or bollards is appropriate for a single shift operation. Traffic cones and bollards are to be spaced in accordance with Table 5.3 and using the speed zone they are in (the 200 m distance beyond a change in speed zone for sign spacing does not apply to delineation – see Note 27). The existing lane width is 3.5 m, and the work area extends to the lane line between the two lanes. From Table 5.3, the 'PAST' edge clearance for traffic cones is 0.3 m (but may be reduced to zero if devices are also used to reduce speeds through lane narrowing). The minimum lane width for the open lane is 3.0 m (Table 2.5). Use an edge clearance of zero to reduce traffic speeds past the site (40 km/h is the speed zone past the work area) and position traffic cones 3.0 m from the existing right-hand edge line to the face of the traffic cones or bollards which should give sufficient space behind the cones or bollards for works to be completed up to the centreline.

• For information regarding work area separation, delineation and clearances, refer to QGTTM Part 3, Sections 5.3 and 5.4.
• For information regarding minimum lane widths, refer to QGTTM Part 3, Table 2.5.
• For additional information regarding the use of supplementary devices at roadworks to reduce speed in Queensland, refer to the Guideline – Traffic Management Works on Roads, Chapter 1, Section 1.
• For information regarding the use of temporary speed humps and rumble strips, refer QGTTM Part 3, Sections 5.5.2 and 5.5.3.

4. QGTTM Part 3 requires safety buffers immediately prior to work zones where the approach speed limit is 60 km/h or greater. The approach speed due to the use of traffic control will likely be 60 km/h (approach speeds have not yet been determined – see Note 5). A safety buffer of 30 m will be provided in this scenario. This site is a high-speed environment and a multi-lane carriageway, so the typical safety buffer length of 20 m to 30 m may be extended up to 100 m. In this scenario, the TMD has determined that there is no reason to extend the safety buffer as the site has good alignment and sight distance. Although not yet determined at this stage, a truck mounted attenuator (TMA) with arrow board in the taper and a long additional warning area (see Note 10) will be provided, which should further improve visibility of the taper and the work area and negate the need to extend the safety buffer.

5. Workers on foot are expected to be within 1.2 m of live traffic and, therefore, require a work zone speed limit of 40 km/h. The 40 km/h speed restriction sign needs to be in place prior to the work area (the Designer has chosen one sign spacing, as per Table 2.2, in advance of the work area). The speed restriction sign is also located clear of the safety buffer as traffic control devices are not permitted in the safety buffer. In this scenario, as the safety buffer is 30 m long, locate the work zone speed restriction sign 15 m into the additional warning area. The location of the 40 km/h speed restriction sign is now known, and we can determine that the safety buffer is actually within a 40 km/h zone (and may not be required by AGTTM); however, the safety buffer is located almost immediately after the 40 km/h sign, so would be within the 200 m zone following a speed reduction and, as such, should still be provided. In this scenario, a safety buffer of 30 m will be provided (see Note 4).

• For information and values of recommended work zone speed limits, refer to QGTTM Part 3, Table 5.5.
• For information and considerations about safety buffers, refer to QGTTM Part 3, Section 5.6.
• For recommended spacing of signs (and between traffic control devices), refer to QGTTM Part 3, Table 2.2, and Figure 2.2.