Coordinate with the TxDOT Project Manager to determine the level of effort and scope of the ICE.

Below is an abbreviated version of an ICE report. It covers the Stage 1 requirements and generates a preferred type of intersection control without requiring more detail that Stage 2 generates. When both the safety (SPICE) and operations (CAP-X) analyses generate a clear preference for intersection control, Stage 2 ICE investigation is not necessary, and the project can proceed to concept design and detailed cost estimation.

Background:

A local agency is proposing intersection improvements. They submitted a white paper to the TxDOT area office, justifying a roundabout.
White paper was forwarded to TxDOT Design Division Roundabout and Alternative Intersection Design (RAID) for review.

Assumptions:

Kept all default settings, no calibration of SPFs or CMFs
AADT: no consistent AADT provided - used peak hour volumes from combined spreadsheet (TIA Analysis) to extrapolate to an ADT and use as AADT to input in the tool:

Total Entering Volume (TEV) =

	US 123	CR 456
AM	1,522	728
PM	1,479	996

Assume*:

US 123 ADT =

1522/.08 = 19025	1479/.08 = 18487
1522/.12 = 12683	1479/.12 = 12325

Average =

15,630

CR 456 ADT =

728/.08 = 9,100	996/.08 = 12,450
728/.12 = 6,067	996/.12 = 8,300

Average =

8,979

Lowest Total Crashes:

(1.55) Unsignalized RCUT
(2.38) Minor Road Cut - don't count per red "No" in table
(2.53) 1-lane roundabout
(2.76) 2-lane roundabout

Lowest Fatal & Injury Crashes:

(0.33) 2-lane roundabout
(0.45) Unsignalized RCUT
(0.51) 1-lane roundabout

Highest Total Crashes:

Traffic Signal
Displaced Left-Turn
MUT and Signalized RCUT

Highest Fatal & Injury Crashes:

Traffic Signal
Displaced Left-Turn
Signalized RCUT

Assumptions:

Used peak hour volumes from combined spreadsheet (CR 456 TIA Analysis)
Did not analyze intersection types not included in SPICE tool (such as Quadrant Road)
Kept all default factors.

Results:

Summary:

Only two intersection types under 1.0 V/C Ratio:
DLT and 2 x 2 Roundabout
Three intersection types very close to 1.0 V/C Ratio:
Signalized RCUT
Multi-lane roundabout (1 lane north-south, 2 lanes east-west)
MUT

Summary of SPICE and CAP-X Analysis:

A 2 x 2 roundabout may provide the best combination of safety and capacity.
A DLT may provide the best capacity but has one of the highest levels of total crashes and fatal/severe crashes.
An unsignalized RCUT has the lowest total crashes, but has a very poor V/C ratio (1.65)
A multi-lane roundabout (1 lane north-south, 2 lanes east-west) is just over 1.0 V/C (1.05) but provides high safety benefits and would be worth consideration.

Comments on White Paper and Roundabout Design:

Traffic
Recommend developing design-year traffic projections - 10 year and 20 year and evaluating roundabout performance for each.
Recommend a review of proposed lane configuration based on traffic analysis.
Design
Design shows geometric problems (listed below) – recommend local agency gets a peer review of the roundabout traffic analysis (for lane configuration) and geometric design.
Exhibit does not give any dimensions, so a review of roundabout size and other geometrics is limited - request a more detailed schematic that includes the following:
Roundabout key dimensions (ICD, entry & exit flare widths, typical lane widths, deflection, and entry curve radii, circulating lane widths, truck apron widths, pedestrian refuge island widths)
Striping
Sidewalk widths
Vertical profiles and roadway cross slopes
Striping as shown does not make sense - circulatory stripe touches the top of the west leg splitter island so lane configuration is unclear.
Limited-to-no deflection on west and south legs - provide better speed control.
Exhibit cuts off north leg, so review not possible.
Pedestrian crossings are too far back - place them 20' back from circulatory roadway.
Recommend documenting and reviewing roundabout performance measures:
Fastest paths - plan view and radius/speed calculations
Truck turning movements - design and check vehicle - plan view.
Path-overlap check for multilane entrances.
Sight distance triangles and calculations
Sidewalk widths seem narrow to be considered a shared use path, but dimensions not so. If less than 10’, need to identify bicycle facilities.
General comment:
Recommending construction in 2024, but ROW acquisition may slow that down.

Review Summary:

Based on high-level analysis, a 2-lane roundabout will likely provide the best combination of safety benefits and capacity, and a multi-lane roundabout (1 lane north-south, 2 lanes east-west) would also be worth consideration.
The roundabout design needs to be looked at much more closely - first on lane configuration based on traffic analysis, and second on the geometrics. Poor lane configuration and/or design may result in a less-than-optimally functioning roundabout.