Business Segment Information - Business Segments (Details)	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Business Segments
Number of reportable segments | segment			3
Total revenues	$ 27,882,000	$ 24,417,000	$ 54,489,000	$ 49,892,000
Depreciation	222,000	198,000	420,000	463,000
Loss on impairment of goodwill	0
Segment income (loss)	(2,351,000)	(1,396,000)	(3,922,000)	(2,988,000)
Product
Business Segments
Total revenues	13,795,000	12,412,000	28,312,000	24,330,000
Service
Business Segments
Total revenues	14,087,000	12,005,000	26,177,000	25,562,000
Operating segments
Business Segments
Total revenues	27,882,000	24,417,000	54,489,000	49,892,000
Segment income (loss)	3,030,000	2,659,000	5,893,000	4,708,000
Operating segments | Product
Business Segments
Total revenues	13,795,000	12,412,000	28,312,000	24,330,000
Operating segments | Service
Business Segments
Total revenues	14,087,000	12,005,000	26,177,000	25,562,000
Operating segments | Roadway Sensors
Business Segments
Total revenues	12,555,000	10,977,000	25,363,000	21,837,000
Segment income (loss)	2,224,000	2,477,000	4,556,000	4,310,000
Operating segments | Roadway Sensors | Product
Business Segments
Total revenues	12,480,000	10,960,000	25,251,000	21,761,000
Operating segments | Roadway Sensors | Service
Business Segments
Total revenues	75,000	17,000	112,000	76,000
Operating segments | Transportation Systems
Business Segments
Total revenues	14,031,000	12,359,000	26,390,000	25,543,000
Segment income (loss)	1,942,000	1,771,000	3,508,000	3,129,000
Operating segments | Transportation Systems | Product
Business Segments
Total revenues	1,315,000	1,452,000	3,061,000	2,569,000
Operating segments | Transportation Systems | Service
Business Segments
Total revenues	12,716,000	10,907,000	23,329,000	22,974,000
Operating segments | Agriculture and Weather Analytics
Business Segments
Total revenues	1,296,000	1,081,000	2,736,000	2,512,000
Segment income (loss)	(1,136,000)	(1,589,000)	(2,171,000)	(2,731,000)
Operating segments | Agriculture and Weather Analytics | Service
Business Segments
Total revenues	$ 1,296,000	$ 1,081,000	$ 2,736,000	$ 2,512,000