The New Zealand Transport Agency (NZTA) has apologised after melting roads coated cars in a sticky black layer.
The brutal summer heat is taking its toll on the bitumen which melts and rises above the chip seal, making the road surface slippery and covering vehicles in gunk.
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"We apologise to customers for the road surface south of the Johnstones Hill Tunnels on Friday afternoon, and to customers who may have experienced bitumen material on their vehicles," a spokesperson said on Facebook.
"Crews are on standby and plans are in place to ensure the road surface remains settled."
But it hasn't placated all motorists, with one person calling it a "cop out".
"Pay to be stuck in traffic AND pay for tar stains on your vehicle," one person commented.
"Probably using the weather as an excuse for the poor build quality of what we actually pay for," another said.
The Johnstones Hill Tunnels stretch of road was one of the worse affected - a problem amplified by NZTA laying fresh bitumen seal down.
Drivers complained of the road surface liquefying and being pulled up off the road.
"I could see the liquid tar flicking off the tyres of the car," one driver told Newstalk ZB.
"As we got further along [going north] towards the tunnels, the road just got shinier and shinier and the tar was just flicking off the tyres like water."
"I saw a brand new Holden plastered up the side where it had flicked off the tyres," another said.
The NZTA was forced to take drastic action, spraying down road surfaces to cool them down.
"Due to high temperatures today and high traffic volume the road surface on State Highway 1 (northbound) near the Johnstone Hill tunnel has reacted," the NZTA said on Friday.
"Water trucks have been deployed to douse the road surface and dampening will continue until temperatures start to drop this evening.
"Dampening the road will reduce the stickiness and will allow traffic to return to normal peak flow. Please note a fresh bitumen seal was recently sprayed on this road. Motorists are advised to take care in the area and be prepared for some delays."
The NZTA says motorists can clean the bitumen on their vehicle using baby oil and kerosene.