Page 53 - Bridge and Highway Structure Rehabilitation and Repair

28 SECTION 1 ADMINISTRATIVE ISSUES

3. Current AASHTO manual for condition evaluation of bridges
4. Current AASHTO policy on design standards: interstate system
5. Current state geometric design policy for bridges

1.9 THE MAINTENANCE AND PROTECTION OF TRAFFIC DURING CONSTRUCTION
1.9.1 Projected Traffi c Count
1. Building bridges is all about solving traffi c issues.

Maintaining and protecting traffic is the primary planning issue. Table 1.6 shows an increase

in maintenance with increased traffic volume. When an existing bridge is to be replaced or

is to undergo major rehabilitation, the decision whether to maintain traffic in the proxim-
ity of the existing bridge or to detour traffic must be made. This decision is based upon

consideration of many conditions, engineering feasibility, cost effectiveness, ADT/truck

traffic, and the impact on the local economy, emergency services, the environmental impact,
and obtaining right-of-ways. Adequate public coordination must be performed in order to
minimize adverse impacts.
2. Construction stages planning

Traffic counts are required for average daily traffic (ADT) volume. A traffic count needs to

be performed to assess the impact on traffi c flow during construction. Warning signs must be

placed weeks in advance so that the users may select an alternate route to avoid congestion.
Local authorities should be contacted to determine if they have any restrictions regarding
lane closures.
Prior to developing staging plans, the agency’s traffic operations department will provide

the maximum allowable lane closure hours in each direction and the maximum number of
lanes that can be closed at one time. An eight to 10 hour night window is required for the
contractor to properly complete his work. Extra hours are permitted for weekend work.
3. Traffic count is needed for

• Planning of the number of lanes
• Fatigue analysis of girders
• Detour purposes
• Posting any weight or speed restrictions
• Widening may be required due to high ADT, congestion and traffi c jams.
4. Using the full detour (bridge shut down) option during reconstruction
Full detour (shown in Figure 1.11) or partial detour plans on adjacent local roads or other
traffic control schemes, if applicable, must be approved by local authorities.

Table 1.6 Classifi cation of daily traffi c.
S. No. Traffic Volume ADT Location Remarks

1 Very low — Rural area bridges serving low Low fatigue and minimum
density population maintenance
2 Low < 4000 — —
3 Medium > 4000 Bridges serving medium Average fatigue and maintenance
< 25000 density population
4 High > 25000 — —
5 Very high — Interstate bridges during High fatigue and maximum
peak traffi c maintenance*
* May require increased inspection frequency