Voters in Arlington County are heading to the polls on Tuesday for a special election to fill the seat vacated by the resignation of longtime County Board member Chris Zimmerman (D).

Democratic nominee Alan Howze is facing John Vihstadt, a Republican who is running as an independent “fusion candidate,” and two lesser-known candidates, Janet Murphy and Stephen Holbrook.

Polling places are open from 6 a.m. to 7 p.m.

Party activists and political observers say the race seems more competitive than any non-primary contest in overwhelmingly Democratic Arlington in at least a decade. No non-Democrat has been elected to the County Board since 1999.

Vihstadt is trying to tap into a strain of dissatisfaction about county spending on projects, such as the Columbia Pike streetcar, and concern that the five-member board, which often votes unanimously, has become too insular.

Howze, for the most part, supports the decisions and priorities of the current board majority, although he increasingly has expressed a willingness to examine spending priorities more closely.

In the last week of the campaign, he pushed Vihstadt to support the expansion of Medicaid in Virginia, which Republicans in the state legislature have resisted.