Intersection prioritization, Otter Mills arterial corridors

Sixteen intersections on Iowa 494, Mill Street, Riverside Drive and Prairie Avenue were scored against five weighted criteria from the draft Safety Action Plan. Iowa 494 & Washington Ave ranks first under every weighting tested, while ranks 2 through 5 depend on the cost weight and on one corrected pedestrian and bicycle count.

Iowa DOT crash data 2021–2025, counts 2023–202516 intersections within city limitsWeights per draft Safety Action PlanPrepared Nov 5, 2026

Summary

Robust priority · INT-03

Iowa 494 & Washington Ave ranks first under every weighting

INT-03 ranks No. 1 in all 3,125 weight combinations with each criterion weighted 1 to 5. It has the highest severity score (17: two KA and seven BC crashes), 690 pedestrians and bicyclists crossing per day, and 310 students on Safe Routes to School walking routes (SRTS walk audit, pp. 12–13).

Iowa 494 is an Iowa DOT route. The project needs Iowa DOT concurrence.

Data issue · INT-09

Riverside Dr & Water St makes the top five only because of one count week

The 870 pedestrians and bicyclists per day were counted Sep 15–21, 2025, while the River Trail was detoured through the intersection during the Mill Race Bridge closure (traffic counts, tab CS-09). With the regular 2023 count of 280 per day, INT-09 drops to No. 9 and Prairie Ave & Ridgeway Dr (INT-13) moves up to No. 5.

The matrix uses the 2023 count. A new count is recommended.

Weight sensitivity · INT-02

The cost weight decides whether Iowa 494 & Ridgeway Dr makes the list

INT-02 ranks No. 2 with the proposed weights but has the widest rank range of any intersection: No. 2 to No. 16. Raising the cost weight from 2 to 4 drops it to No. 6, because the $4,140,000 roundabout reconstruction is the most expensive project in the matrix (cost estimates, row 5).

Prioritization matrix

Adjust the weights to re-rank the intersections on the map and in the list. Click an intersection or a value in the matrix to see the source behind each score. The Sensitivity tab shows how stable the ranking is.

Weighting

Corridor map

Number shows the rank
Rank 1–5 Rank 6–10 Rank 11–16 Flagged count State route City street

Ranking

Score 0–100, change from proposed weights

    Source value and 0–100 score per criterion. Rows below the dashed line are outside the top five.

    Sources and method

    Sources

    • IowaDOT_Crash_Data_OtterMills_2021-2025.xlsxIowa DOT crash records within 250 ft of each intersection center, 2021–2025, with KABCO severity216 crashes
    • Traffic_Counts_OtterMills_2023-2025.xlsxCity tube counts (entering AADT) and pedestrian and bicycle counts, one tab per count station16 stations
    • OMT_AVL_Stop_Events_Spring2026.csvOtter Mills Transit AVL stop events, Routes 1–7, Mar 2–May 17, 202611 weeks
    • OMCSD_SRTS_Walk_Audit_2025.pdfSafe Routes to School walk audit for six schools, with the enrollment projection for the new North Elementary (opens Aug 2027)38 pages
    • Planning_Level_Cost_Estimates_2026.xlsxProposed countermeasure and planning-level cost per intersection, 2026 dollars16 rows
    • Otter_Mills_Safety_Action_Plan_Draft_2026.pdfPrioritization framework the proposed weights are based on (p. 14)46 pages

    Method

    1. All intersections on the four arterial corridors within city limits were included, 16 in total, with jurisdiction and traffic control.
    2. Source values per criterion: severity score = 5 × (K + A crashes) + 1 × (B + C crashes); bus delay = weekday bus trips × average delay through the intersection; pedestrians and bicyclists crossing per weekday; students whose SRTS walking route uses the intersection; planning-level countermeasure cost.
    3. Each criterion was normalized to 0–100 between the lowest and highest value among the 16 intersections. For cost, the lowest cost scores 100.
    4. The total score is a weighted average: the sum of weight × score divided by the sum of the weights. The severity score is the draft plan's own simplified index. It is not the Highway Safety Manual's EPDO score, which weights each crash by its cost relative to a PDO crash and gives fatal and serious injury crashes far more weight than 5 to 1. The proposed weights (5, 3, 4, 3, 2) follow the Safety Action Plan's Safe System priorities: fatal and serious injury crashes first, then vulnerable road users, transit and school routes.
    5. Counts were checked against the notes in the count file. One count taken during a detour was flagged and replaced with the most recent regular count.
    6. Sensitivity was tested by re-ranking all 3,125 combinations of weights 1 to 5.

    Assumptions and limitations

    • PDO crashes are listed and included in the crash rate but not in the severity score. Bicycle-only falls are not in the police crash data.
    • Normalization is relative. Scores apply to these 16 intersections and change if intersections are added or removed.
    • Costs are planning-level estimates without design, in 2026 dollars. They have not been checked against Iowa DOT bid prices; a cost estimator should confirm them before the cost criterion is used to decide.
    • Projects on Iowa 494 (INT-01 to INT-04) need Iowa DOT concurrence. How responsibility is split between the city and Iowa DOT on a primary road extension inside city limits has not been checked in detail and should be confirmed with the Iowa DOT district office. Funding shares and grant eligibility are not part of the matrix. Nor are expected crash reductions from crash modification factors (CMFs) or benefit–cost ratios; those belong to the project development step.
    • Student numbers for INT-05 and INT-08 are based on the district's enrollment projection for North Elementary; the others come from the walk audit's parent survey.